Why bake result have some broken line?

my step is

1.import model,and selet all mesh

2.switch to edit mode,then use uvwarp/smart or uvwarp/lightpack

3.bake. combind.

and got this result. how to improve this result?

789.blend (1.2 MB)

Diagonal UV lines will have bleed from adjacent pixels and so need padding. Though fixing that alone won’t give perfect results.
If that’s the result of a smart unwrap then the faces are likely not connected to their neighbors so you should do a merge by distance operation and convert the tris to quads before doing another smart unwrap.

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thank you ,I’ll try.