In this paper, the hemicelluloses was extracted by alkali from aspen, then it was made to be surface enhance agent by cationic modification. The original and modified hemicelluloses were characterized by FT-IR and GC. The effect of hemicelluloses species, content and treatment time on the strength of paper were studied. The results showed that the optimum content of cationic hemicelluloses for surface enhance was 6% at 35°C for 15s. In the conditions, the tensile strength and crushing strength were increased by more than one time. Compared with the original hemicelluloses, when substitution degree of the cationic hemicelluloses was higher than 0.03, the modified hemicelluloses with better quality of surface enhance.