I want to use rotateonaxis to rotate 180 degrees

Questions
1

A lot of methods have been tried, not really 180 degrees

https://jsfiddle.net/a6965921/ky2h9xdn/10/ 这个my case

2

Do you want to achieve this? https://jsfiddle.net/f9thn7jL/

Keep in mind that the axis vector needs to have unit length. So your code:

meshgroupss.rotateOnAxis(new THREE.Vector3(1,1.2,0),180* Math.PI / 180)

does not work. You have to call .normalize() on the first argument.

Also the computation for the second argument makes no sense. Just use Math.PI.