In order to solve the contradiction between processing fluidity and mechanical strength of silica reinforced liquid silicone rubber， three kinds of fumed silica with typical structural characteristics were used as reinforcing fillers of silicone rubber. By means of particle size analysis of silica， rheological and mechanical properties test of silicone rubber and atomic force microscope analysis， the effects of surface characteristics and aggregation structure on rheological and mechanical properties of silicone rubber were comparatively studied and analyzed. The results of particle size analysis and atomic force microscope analysis show that fumed silica HT200 with organic surface modification and optimized aggregation structure has smaller aggregation structure size and more uniform particle size distribution. The results of rheological and mechanical properties analysis show that HT200 has the weakest tackifying effect on liquid silicone rubber among the three kinds of silica. When the amount of HT200 is 50 phr， the viscosity of the compound is 1045 Pa·s， which is significantly lower than that of the liquid silicone rubber filled with IPC300 and R812S with the same amount. Meanwhile， the silicone rubber has excellent tensile properties， and the tensile strength and elongation at break are 8.2 MPa and 1590 % respectively. The results show that the organic modification of silica surface and the optimization of aggregation structure can obviously improve the dispersion uniformity of silica in liquid silicone rubber， reduce the tackifying effect of silica， and effectively coordinate the contradiction between rheological properties and mechanical properties of liquid silicone rubber， which has important reference significance for the design of high-performance liquid silicone rubber formula.