In order to study the influence of rubber powder on the mechanical properties and microstructure of styrene acrylic emulsion modified concrete（SEMC）, 45 cubes of 150mm×150mm×150mm and 45 prismatic specimens of 150mm×150mm×300mm were prepared. Compressive strength, stress strain curve, elastic modulus and Poissons ratio of SEMC were determined and the influence of rubber powder added on interface and microscopic structure of SEMC was analyzed by scanning electron microscope（SEM）. The results show that the stress strain curve of SEMC is similar to that of ordinary concrete. As the polymer cement ratio increases, the peak strain and the Poissons ratio increases, while the compressive strength and the elastic modulus decrease. After the rubber powder is mixed, the peak strain and the Poissons ratio increases, while the strength of rubber powder styrene acrylic emulsion modified concrete(RPSEMC) and the elastic modulus decrease. The styrene acrylic emulsion film formation and the cement hydration product form a dense network structure. Slip caused by filmforming of acrylic emulsion destabilizes concrete; the “hole” effect of the rubber powder and the presence of the rubber cement interface make the strength of the SEMC decrease, and the deformation energy absorption of the rubber powder is the damping energy of the concrete.