How do I remove these lines？

[ice]

the red lines，Split body produce。
How to remove quickly, or not produce？

[PEC]

Try replace face?

[ice]

I try ,but not work

[jean-philippe2]

can you share the file ?

[Bob3DPO]

Hi @ice , It looks like this was a gear where you split then removed a piece.

After you Replace Face as @PEC suggests, can you delete one of the faces? Sometimes you don’t have to replace face, but often you do. See this video with an “octagon gear”