To solve the problems of slow swelling, high viscosity and high processing difficulty and high viscosity of traditional rubber asphalt, the crumb rubber was highly degraded(soluable content(by mass) >50%) by using twin screw extruder to break the cross link network in rubber and modify the asphalt. The effect of the types and content of additives on the processing properties and rheological properties of highly degraded rubber asphalt was investigated by conventional asphalt test and dynamic mechanical analysis. The results show that the highly degraded crumb rubber can be dissolved in asphalt efficiently meanwhile the processing and its rheological property are improved. The tire source and content influence the rheological properties of modified asphalt. The increased content of the additive strengthens the improving effect. The maximum content of reclaimed crumb rubber reaches 50% without great increase of the processing viscosity.