This paper is special in modifying effects of styrene butadiene emulsion D623 on mechanical properties of cement mortar used for the surface repair of bridge on the base of German standards and specifications. It has shown that the polymer emulsion D623 reduces content of mixing water, effectively enhances both flexural strength and tensile bond strength, largely decreases the ratio of compressive strength to flexural strength, while improves the ratio of flexural strength to elastic modulus. In conclusion, taking the combination of mechanical properties of modified mortar, such as compressive strength, flexural strength, tensile bond strength and elastic modulus, the appropriate addition of polymer emulsion D623 to modified mortar for the use of bridge repair ranges from 10.0% to 17.5%.