The surfaces of carbon fiber sheet and aramid fiber sheet were modified respectively by using of nitric acid, coupling agent and plasma. The sheets were then bonded to cement mortar externally, which called FRP-cement mortar. The flexural properties of FRP-cement mortar were investigated by 3-point bending test. The results show that the flexural properties of cement mortar are improved greatly by bonding carbon fiber or aramid fiber sheets. Their maximum loads increase more than 150%, and fracture modes are changed from brittleness to the accumulation breaking with ductility. The maximum loads and toughness indexes of CFRP-cement mortar and AFRP-cement mortar increased obviously after carbon and aramid fiber sheets were modified by means of plasma. When the specimens are bended, they are tensile fracture, which indicates that the high strength of fibers is fully utilized.