Abstract: In order to improve the electrical tree resistance of polypropylene (PP), montmorillonite (MMT)/PP composites were prepared by one-step and two-step melting intercalation processes, in which the organic MMT as the nanophase and the maleic anhydride grafted polypropylene (PP-g-MAH) as the compatibilizer. The crystallization morphology and crystallization process of PP and MMT/PP composites were studied by polarizing microscopy (PLM) and differential scanning calorimetry (DSC) curves. SEM was used to observe the dispersion state of MMT in composites. The influence of preparation process and crystallization morphology on property of electrical tree resistance was investigated by electrical tree initiating test. The test results indicate that the inorganic phase disperses more uniformly, crystallization size decreases and the spherulites become into lamellar crystallization stacks in MMT/PP composites which was prepared by two-step melting intercalation process, and the degree of crystallinity increases about 2.7%. The length of electrical trees are longer and it has less divarication in PP specimen, and characteristics of shorter and denser shape with more divarication are found in PP/MMT samples.