The phase behavior of blends of SAN/PVME in film is studied by Time-resolved Small-angle light scattering (SALS) and Atomic force microscopy (AFM). The phase diagram shows that both SAN99 (styrene volume fraction is 0.99)/PVME and SAN97 (styrene volume fraction is 0.97)/PVME have the lower critical solution temperature (LCST), the LCST of SAN97/PVME is (117℃) lower than that (119℃) of SAN99/PVME, and the cloud points of these two systems are hard to be obtained before the decomposition of PVME when the weight fraction of SAN (SAN99 or SAN97) is more than 50 wt%. For 20/80 SAN97/PVME and 20/80 SAN99/PVME blends (80 wt% PVME), although the experimental temperature is higher than the phase separation temperature, the phase separation does not take place immediately. It takes a period of time before the phase separation. The AFM phase images of 20/80 SAN99/PVME blend show that, as the phase separation proceeds, very small SAN99-rich droplets appear, the droplets become large step by step, then two large droplets coalesce into one larger droplet, and the obtained droplet size distribution is broader. Both SALS and AFM results show that, during the phase separation, the very small orientation of SAN domains takes place at the early stage of phase separation, and finally disappears when the phase separation finishes.