Recently,many multiscale methods built purely on the kinetic theory of gases have been proposed to simulate gas flows [1,2].In these methods,the same evolution equation is solved to obtain kinetic level information through the molecular velocity distribution function.Information exchange at coupling interfaces between two flow regions resolved with different meshes in the velocity space becomes easy.A key issue is to find breakdown parameters that can determine suitable resolution of velocity-space discretization to satisfy requirement on modelling accuracy.As the same kinetic level information is available through the molecular velocity distribution function,it is now feasible to establish new breakdown parameters utilizing information at the kinetic scale rather than macroscopic flow quantities alone.