I've tried to use smooth modifier, it always cause another distortion problem.You may be able to do a simple fix with delta smoothing. If your model doesn't already have a smoothing modifier, go to edit/geometry/add smoothing modifier. In your parameters tab find the smoothing modifier, set the mode to 'base shape' and increas the itteration from 7 to 45, beyond that and all your joints will look a bit too gooey. this isn't a proper fix, but it will make the shaping more consistent, it's usually the fix I use cuz I'm too lazy to do much more than that.
Sorry to get back to you so late,I do have bend control working , it seems like these disortions causing by bending too much,and I tried every slider in morphing body ,none of those correcting the area where disortions appeared , I consider that these disortions are unfixable. Thank you for all the help !okay try this
Bend Control for Genesis 3 Male(s) & Female(s)
https://f95zone.to/threads/bend-control-for-genesis-3-male-s-female-s-unofficial-bundle.23158/
Bend Control Bundle for Genesis 8 Female(s) and Male(s)
https://f95zone.to/threads/bend-control-bundle-for-genesis-8-female-s-and-male-s.20282/