Multivariate composite modifier (MCM) was successfully prepared by blending out method and was used to modify waste high density polyethylene (WHDPE), while the effect of MCM addition on comprehensive performance of WHDPE composite system was studied. The results showed that the impact strength of composite system increased significantly, and the tensile and bending strength decreased with the increase of MCM addition. The increase amplitude of impact strength and the decrease amplitude of stretch and flexural strength were both reduced when MCM added quality score was over 10%. Melt index of composite system was generally in the trend of decrease with the increase in MCM addition, but the increase of MCM addition had no obvious influence on the fusion, crystallization behavior and thermal stability of composite system. The impact section of composite materials had obvious ductile fracture characteristics with the increase of MCM addition. However, with more than 10% of added MCM, reunion phenomenon occurred in the section and the characteristics of ductile fracture gradually began to disappear.