The phase behavior of near-critical PVME/SAN blend in thin film was studied by time-resolved small-angle light scattering (SALS) and atomic force microscopy (AFM). The phase diagram showed that PVME/SAN99 blend had the lower critical solution temperature (LCST), the LCST and the critical composition was 119 °C, 74 wt.% PVME, respectively. However, the cloud points of this system were hard to be obtained before the decomposition of PVME when the weight fraction of SAN99 was more than 50 wt.%. Both SALS and AFM results confirmed that, for PVME/SAN99 blend, there was certainly a transition from homogeneous nucleation and growth to nonlinear spinodal decomposition in the twophase region of 3D Ising regime. For 80/20 PVME/SAN99 blend, during the phase separation, the small orientation of SAN99 domains took place at the early stage of phase separation, and finally disappeared when the phase separation finished. But for 70/30 PVME/SAN99 blend, the orientation did not appear.