Abstract: To analyze the microstructure changes of different types of crumb rubber under different twin-screw extrusion processes, including internal substances, molecular weight and characteristic functional groups, as well as the impact of microscopic factors on the activation degree, car tires and truck tires were taken as raw materials. Activated crumb rubber was prepared by adjusting the twin-screw extrusion process （the amount of activation additives and the activation temperature）. The solubility （activation degree） of the crumb rubber was measured by the Soxhlet extraction method. Combined with TGA, GPC and FTIR, the influence mechanism of the changes in microscopic parameters on the activation degree of crumb rubber under different process conditions was analyzed. On this basis, the grey relational analysis method was introduced to quantify the macro and micro factors affecting the activation degree of twin-screw extruded rubber powder. It was shown that the content of soluble substances reflected the degradation degree of crumb rubber during the activation process and was positively correlated with the activation degree. The weight-average molecular weight and the proportion of large molecular weight revealed the essence of crumb rubber activation from the aspect of molecular chain breakage. With more molecular chains broken, large molecular weight substances dropped into the sol, and the weight-average molecular weight and the proportion of large molecular weight increased, along with the improvement of the activation degree. The decrease in the peak intensity of the main chain and cross-linking bonds indicated that the breakage of chemical bonds during the activation process was crucial for the recovery of the reaction activity of crumb rubber and was highly correlated with the activation degree. Grey relational analysis shows the descending order of factors affecting the activation degree of crumb rubber from truck tires is as follows: weight-average molecular weight, processing temp, soluble substance content, cross-linking bond peak intensity, main chain peak intensity, proportion of large molecular weight, desulfurization additive amount, and for car tire crumb rubber is: processing temp, proportion of large molecular weight, weight-average molecular weight, cross-linking bond peak intensity, soluble substance content, main chain peak intensity, desulfurization additive amount.