Clipping plane sub d

why my clippingplane look like this esspecially when im using sub d model

It seems your model is quite big and/or far from the origin.
Can you move your entire project nearer the origin?
Or, can you scale it to use a different unit?

Graphic glitches often are related to using too big coordinates for the geometries.

Yes, my project is quite large because it is for a college assignment. I have tried both methods you recommended, and the result is better, but some lines still look like that.

Hard to guess without the file.
What is your SystemInfo?
Can you upload your file?

test - Google Drive can you check this

I see no problem here.
Paste your SystemInfo here.

The problem with large distances from the origin does not lie with Rhino—since it performs calculations using 64-bit double-precision floating-point numbers—but rather with graphics cards, as they only support 32-bit single precision; something finally needs to happen on this front among the developers at AMD and Nvidia.