I want to make a sowrd slash like effect,roughly like this https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.artstation.com%2Fartwork%2FD89A0&psig=AOvVaw1Xrkkof2L2CgfqXMFUUIZb&ust=1605402557031000&source=images&cd=vfe&ved=2ahUKEwjWiqva7IDtAhWYD1kFHYKQDW8QjRx6BAgAEAc​​

I use a curved mesh as the path,my question is how to make the dynamic effect,that is, show only part of the mesh and move this part from start to end,

One approach might be to limit and animate the UVs of your mesh, rather than animating the mesh itself.

So, for example, you might have a texture that starts off transparent, increases opacity, then becomes transparent again.

To start with, you might set your mesh's UVs to cover only the start of the texture, thus making it transparent. During the slash, you would then on each frame adjust the UVs of the mesh such that they move through the texture, giving the impression of the slash advancing, then disappearing into the transparency at the far end of the texture--before the whole thing is reset for the next slash.

@Thaumaturge I also came up with this idea,and I am considering using 2 textures,one for color and one for alpha to get more variation.

Using two textures sounds like a good idea, indeed. ^_^