The structure, composition and mechanical properties of new compatibilizer polypropylene-polyethylene block copolymer (iPP-b-PE) were studied by carbon nuclear magnetic resonance spectroscopy, wide-angle X-ray diffraction (WAXD) in-situ and tensile tests. The effects of iPP-b-PE on the mechanical properties of PP40/UHMWPE blends were investigated using iPP-b-PE compatibilized melt blown polypropylene (PP40) and ultra-high molecular weight polyethylene (UHMWPE). Fixing the mass ratio of PP40 to UHMWPE at 8∶2 and other conditions unchanged, the addition of iPP-b-PE increased from 1% to 9%. The results show that the molar ratio of PE to PP in iPP-b-PE is 6∶4, and the elongation at break is 2 300%. The addition of iPP-b-PE compatibilizer has little effect on the melt index of the blend, but increases the elongation at break of the blend, and makes the glass transition temperature of PP and UHMWPE close to each other. IPP-b-PE compatibilizer can improve the compatibility between PP and UHMWPE and improve the toughness of the blends.