Correct

然后 vs 以后

/ ránhòu vs yǐhòu /
Strokes

Definition

然后 is an Adverb of Conjunction and 以后 is a Noun of Time, which both means [then; after; afterward].

Example

然后 is an adverb of conjunction and can be used in a complex sentence.
1) Example ① is applied to the future and example ② to the past.

2) 以后 is a noun of time and can form a phrase with a verb or phrase,e.g. 吃饭以后 (after dinner), 毕业以后 (after graduation), 从那以后 (since then), etc. 然后 cannot be so used.

3) In example ② there is a pause between 去买东西 and 然后. If 以后 is used, it follows 买东西 without a pause.
1
Zánmen
咱们
xiān
xué
学习
xiǎoshí
小时
  
,
ránhòu
然后
zài
tǎolùn
讨论
  

Let's first learn it for an hour, and then discuss it.

2
zuótiān
昨天
shàng
上午
xiān
mǎi
dōng
东西
  
,
ránhòu
然后
cái
lái
jiā
我家
chīfàn
吃饭
de
  

After he finished his shopping on yesterday's morning, he came to my place for dinner.

以后 can be followed by a clause.
3
毕业
hòu
以后
  
,
dào
jiā
gōng
公司
gōngzuò
工作
  

He works in a company after graduating.

以后 can function as an Attributive, Adverbial, Subject, and Object.
然后 cannot be used in these cases, 以后 in example ⑤ can also be seen as an adverbial but cannot be replaced by 然后. There is usually a clause in front of 然后 (as in example ① and ②).
4
hòu
以后
de
zi
日子
huì
yuèláiyuè
越来越
hǎo
de
  

The future life will be better and better. (as attributive)

5
hòu
以后
zài
méi
lái
guò
  

Afterwards, he has never been here. (as subject)

6
Huánbǎo
环保
xiàng
项目
  
,
dàn
不但
yào
wéi
dāngqián
当前
服务
  
,
háiyào
还要
duō
wéi
hòu
以后
kǎo
考虑
  

The environment project should not be only for the present, but also for the future. (as object)