Correct

上刀山,下火海

/ shàng dāo shān xià huǒ hǎi / 
Strokes
https://i.cchatty2.com/filters:format(webp)/fit-in/684x0/img/202102/上刀山下火海-Chinese-idioms-Cchatty-407934e0-c455-478f-b6db-16ef72819172-1612776167.jpg

Collocation

1
用不着上刀山,下火海
2
就是让他上刀山,下火海,他也愿意

Definition

上刀山,下火海

Literally means:

explore mountains of swords and seas of flames

Actually means:

do a most dangerous and difficult thing

It means one is so brave as to do difficult or dangerous thing regardless of his own safety. It carries a sense of exaggeration.

比喻不顾自己的安全去做艰难而危险的事情。带有夸张的意味。

Example

Used as predicate or object. (作谓语、宾语)
1
Tā
他
yǒnggǎn
勇敢
jīzhì
机智
  
,
jiùshì
就是
shàng
上
dāoshān
刀山
  
,
xià
下
huǒhǎi
火海
  
,
yě
也
huì
会
píngān
平安
dì
地
huílai
回来
de
的
  
。

He is brave and witty, that is, up the knife mountain, under the sea of fire, will also come back safely.

2
Zhǐyào
只要
néng
能
zhuā
抓
dào
到
shāhài
杀害
tā
他
qīnrén
亲人
de
的
zuìfàn
罪犯
  
,
nǎpà
哪怕
shì
是
ràng
让
tā
他
shàng
上
dāoshān
刀山
  
,
xià
下
huǒhǎi
火海
  
,
tā
他
yě
也
yuànyì
愿意
de
的
  
。

As long as he can catch the criminal who killed his loved ones, even if it is to let him go up the knife mountain, under the sea of fire, he would like to.

3
Wǒ
我
yào
要
nǐ
你
zuò
做
de
的
shì
事
yī
一
diǎn
点
yě
也
bù
不
wēixiǎn
危险
  
,
yòngbuzháo
用不着
shàng
上
dāoshān
刀山
  
,
xià
下
huǒhǎi
火海
  
,
zhǐyào
只要
nǐ
你
bǎ
把
yānjiǔ
烟酒
jièdiào
戒掉
jiù
就
háng
行
le
了
  
。

What I want you to do is not dangerous at all, do not need to go up the knife mountain, under the sea of fire, as long as you give up smoking and drinking on the line.