Abstract: To study the bending behaviors of ancient building timber beams strengthened with near-surface mounted FRP sheets, three groups of eighteen specimens under static loading tests were designed. The reinforcement effects of two ways of replacing damaged members with new ones and with NSM FRP reinforcement were compared. The effects of different types, thicknesses, and lengths of FRP sheets on the bending performance of timber beams were analyzed. The research results show that the ultimate bearing capacity and flexural rigidity of strengthened beams are much higher than that of the unstrengthened simulated damaged ones. Compared with the intact beams, the bending behaviors of optimal strengthened ones are equivalent to that of the intact ones. The bending mechanical properties of bending plate with the same thickness of the CFRP sheets strengthened beams are superior to that of the GFRP sheets strengthened beams. With the FRP sheets thickness, reinforcement length increases, the flexural performance of the strengthened beams can be significantly improved. For the reinforced beams, GFRP sheets outperformed CFRP sheets in terms of concerted performance of the timber, the carbon plate glue and the fiber panel. The strain distribution of reinforced beams along the section height direction of the beam conforms to the plane section assumption on the whole. A calculation model for predicting ultimate moment capacity of pine timber beams strengthened with FRP was put forward, and the calculated results agree well with the observed data.