The invention discloses a composite sound-insulation material and a preparation method thereof. The composite sound-insulation material is composed of the following components in percentage by mass: 65-75% of reclaimed steel slag powder, 10-20% of reclaimed polyethylene, 5-10% of linear low-density polyethylene, 2.5-5% of high-polymer compatilizer, 1-2% of diluter, 1-2% of coupling agent and 0.5-1% of antioxidant. The preparation method comprises the following steps: metering and preparing materials, sequentially adding the materials, dispersing at high speed, banburying, plastifying, extruding, calendering and the like. The steel scrap slag and waste plastic are recycled, thereby implementing reutilization of the waste resources. The composite sound-insulation material has the advantages of low cost, high constructability and the like, is easy for secondary processing and applicable to sound insulation treatment of irregular objects.