At constant temperature and pressure, on which factor does diffusion of gases depend

The size of the molecules would still influence the diffusion. Smaller molecules will have a higher RMS speed, and will diffuse faster than larger molecules, I believe.

beside temperature and pressure, volume largely affect gases.
if volume increase in a particular area, the concentration decreases there. So gas from high concentrated area will diffuse into the previously mentioned part...

The question is very vague though, be specific!!! there might be other factors as well