What the differences between 开心 and 高兴

As a local Chinese, I can tell you that there is no difference IN REAL LIFE between these two words.

The words 开心 (kāixīn) and 高兴 (gāoxìng) are both used in Chinese to describe the feeling of happiness, but there is a subtle difference between the two. 开心 is used for more lighthearted or casual feelings of happiness, while 高兴 is used for more intense or elevated feelings of happiness.
More specifically, 开心 (kāixīn) has a more lighthearted and casual connotation and is often used to describe a temporary or short-lived feeling of happiness. For example, "我听到好消息，开心得不得了" (wǒ tīngdào hǎo xiāoxī, kāixīn de bùdéliǎo) which means "I'm so happy because I heard some good news." 高兴 (gāoxìng), on the other hand, has a more elevated or enthusiastic connotation and is often used to describe a longer-lasting or more intense feeling of happiness. For example, "我的女朋友答应嫁给我，我非常高兴" (wǒ de nǚpéngyǒu dāyìng jià gěi wǒ, wǒ fēicháng gāoxìng) which means "I'm very happy because my girlfriend agreed to marry me."

开心 (kāi xīn) and 高兴 (gāo xìng) as Adjectives are both words that can be translated as "happy" in English, but they have slightly different connotations.

开心 (kāi xīn) is often used to describe a lighthearted, cheerful mood, such as when someone is having fun or feeling content. For example:
我很开心，因为我今天得到了一份新工作。
(Wǒ hěn kāi xīn, yīn wèi wǒ jīn tiān dé dào le yī fèn xīn gōng zuò.)
I am very happy because I got a new job today.

高兴 (gāo xìng) is a more general term for happiness and is often used to describe a more elevated or intense feeling of joy. For example:
我高兴的喊出声来，因为我今天中了大奖。
(Wǒ gāo xìng de hǎn chū shēng lái, yīn wèi wǒ jīn tiān zhòng le dà jiǎng.)
I am so happy that I shouted out loud because I won the big prize today.

So, in summary, "开心" (kāi xīn) is often used to describe a more casual or lighthearted feeling of happiness, while "高兴" (gāo xìng) is used to describe a more intense or elevated feeling of happiness.

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"开心" (kāi xīn) and "高兴" (gāo xìng) also are Verbs, and 高兴 means "like; be interested in doing sth." 开心 means "make fun of; amuse oneself". For example:
别拿我开心了。
(Biè ná wǒ kāixīn le.)
Don't make fun of me.

我高兴去哪儿就去哪儿。
(Wǒ gāoxìng qù nǎr jiù qù nǎr.)
I'll go wherever I want.

There are not interchangeable, here.

there are No big differences.
高兴 means happy/glad/ delighted
开心 = happy; joyful

1，开心 and 高兴 both an Adjective.
今天玩得很开心（高兴）。(Have a good time today.)

2，高兴 is also a Verb, so 高兴 + Object, 开心 can not be followed by Object,
他高兴去帮助别人。(He is happy to help others.)

3，开心 means a joke, 高兴 has not this meaning.
他总是拿别人开心。(He always makes fun of others.)

4，高兴 means willing to do something, 开心 has not this meaning.
他高兴去哪儿就去哪儿。(He can go wherever he wants.)

高兴 and 开心：both of them can be either adj. or verb, and in most of the cases they are interchangeable.
Slight difference is that 开心 is more oral, when it is a adj. Big difference between 高兴 and 开心 when they are verbs: 开心 can have the meaning to make a joke about sb.(高兴 doesn't have such meaning) Eg. 不要拿他开心（Don't make fun of him.）
Both of them can have the format ABAB: 高兴高兴 开心开心（when they are adjs. or verbs）

开心，打心底的高兴，比较长久一些。我们可以说：希望你开心一些。
高兴是暂时表现出来的内心的快乐。我们可以说：你瞧，那个孩子高兴得又蹦又跳。

开心跟高兴是一样的，都是形容词
真（开心）真（高兴）
用法是差不多一样的

Both mean happy and there are no big differences when it comes to daily usage, but there are some slight differences in meaning though.
高兴 = happy; glad; delighted
describe a emotional state of being delighted
开心 = happy; joyful
metaphorically describe an effect of being happy

Also 高兴 is more formal

You should search on YouTube for the same question, there are a lot of videos on the topic.

Actually 高兴 and 开心 are very similar, both of them mean happy, but little bit different.

高兴means happy and exciting.

儿子考上大学了，他特别高兴。

He was very happy and exciting that his son had been admitted to university.

开心 means happy mood.

我很开心能和你一起共进晚餐。

I had happy mood to have dinner with you

Both of 高兴 and开心 have other meanings.

高兴means like to do something.

Ex: 他就是高兴去看电影。 He likes to watch the movie.

In some specific situation, 开心 means make yourself happy by teasing others.

Ex: 别拿他开心。 Don't tease him