The invention relates to a modified asphalt wrapping film bag and a preparation method thereof. The main agent is composed of the following components in the percentage by weight: 55-85% of plastic, 3-25% of rubber and 5-20% of property reinforcing agent; auxiliary agent is composed of lubricant accounting for 0.3-3.0 wt% of main agent and antioxidant accounting for 0.05-1.0 wt% of main agent; property reinforcing agent is polyolefin filled master batch which takes polyolefin as a carrier and takes talcum powder, silicon dioxide or carbon black as a filled master batch; the lubricant is paraffin, stearic acid or calcium stearate; the antioxidant is phenol or amine antioxidant. The preparation method is as follow: at the temperature of 170-220 DEG C, performing mixed granulation; extrudingand blowing film at the temperature of 170-210 DEG C to blow a film with the thickness of 0.06-0.08 mm, wherein heat-resistance temperature is 165 DEG C; when being filled modified asphalt at the temperature of 155-160 DEG C, the modified asphalt wrapping film bag can not be damaged or broken and can be mixed with modified asphalt at the temperature of 180 DEG C, and the preparation method has the characteristics of convenient operation and no environment pollution.