The crystallization and the phase morphology of polypropylene/poly(methy methacrylate)(PP/PMMA) incompatible blends were studied by using polarizing microscopy and discrepancy microscopy.Polypropylene-g-malaie anhydride(PP-g-MAH) was used as a compatibilizer for PP/PMMA blends，the results from the polarized micrographs showed that PP crystalline form became incomplete and PP crystal size decreased because of the crystallization of PP conquering more energy barrier. The results showed that the compatibility of PP and PMMA phases became better，and the interface areas between PP and PMMA phases became unclear in the PP/PMMA/PP-g-MAH blends.When the MAH graft yield of PP-g-MAH was increased，the size distribution of PMMA phase became uniform and the size of PMMA phase decreased.When the graft yield of PP-g-MAH was 2.41 wt% and the concentration of PP-g-MAH in PP/PMMA/PP-g-MAH blends was 4.71 wt%，the size of PMMA dispersed phase showed a minimum value.PP-g-MAH was a reactive compatibilizer，on the one hand，PP segments of PP-g-MAH and PP homopolymer were crystallized together; on the other hand，the acid anhydride groups of MAH were linkaged with the ester groups of PMMA by covalence.The conformation of PP-g-MAH in the interface between PP and PMMA phases decreased the whole system entropy and improved the compatibility of PP/PMMA blends.PP/PMMA and PP/PMMA/PP-g-MAH blend was isothermal crystallized at 130℃.The polarized micrographs showed that the PP crystallization for the PP/PMMA blend exhibited the characteristics of homogeneous nucleation; and PP crystal size for PP/PMMA blends was larger than that for PP/PMMA/PP-g-MAH blend.PMMA phase size for PP/PMMA blend after isothermal crystallization at 130℃ was obviously larger than the corresponding PMMA phase size under non-isothermal crystallization.