In order to improve the performance and to explore the mechanism of rubber asphalt under different reaction conditions. Viscosity, FTIR and GPC test methods were used to study the reaction parameters and the internal reaction mechanism of CRM binders. The viscosity model of different process parameters, which can be used to obtain the optimum parameters, was established by using quadratic polynomial regression analysis. The results show that CRM content is the main factor affecting viscosity of rubber asphalt, the viscosity increase as the CRM content increase. There is mainly physical reaction in rubber asphalt when the temperature is low, yet a weak chemical reaction also appears. However, rubber asphalt react violently when the temperature is high, which can generate new functional groups, namely C—O—C at 109336 cm-1 andC—O—C at 126156cm-1 respectively. The GPC tests show that LMS value of rubber asphalt increase significantly compared to the base asphalt. LMS increases as the temperature increases, so does CRM content. Besides, there is a good correlation between LMS and the viscosity of rubber asphalt.