This study aimed at investigating the dependence of the ultrasonic (US) effects on the structure and properties of the polymer mixtures with different viscosity values. It should be noted that in the current study, polypropylene and high-pressure polyethylene of different brands were selected. The polymer composite materials (PCM) of various compositions treated with and without ultrasound were used. The formation dependence of the phase structures of polyolefin compositions on composition and viscosity of polymer systems was established. The regularity "structure-properties" of modified mixtures of polyolefins was determined. The influence of ultrasonic on the restoration process of the structure and the formation of new chemical bonds in polyolefin mixtures was discussed. The structure of the compositions of the polymer and technological conditions for their processing, which providing high physical and mechanical characteristics of PCM, were also proposed. The results indicated that to create compositions with high physical and mechanical characteristics, it is recommended to use a mixture of polyolefins containing 70% PE, modified by ultrasonic treatment.