The invention provides an osteotomy plate and a tibial osteotomy method. The osteotomy plate comprises a fixing plate and a guide plate. The guide plate is connected with the fixing plate and is protruded out of the fixing plate along the direction which is perpendicular to plate surfaces of the fixing plate, and an osteotomy groove is formed in the guide plate along the directions of the plate surfaces of the fixing plate. According to the technical scheme, the osteotomy plate and the tibial osteotomy method have the advantages that the osteotomy plate is simple in structure and is light, the single tool can have functions of four or five tools in the prior art, and accordingly osteotomy operation can be simplified; the osteotomy plate is in an integral design, accordingly, cracking risks in osteotomy procedures due to diversified welding tools can be prevented, and the problem of osteotomy termination due to breakage of osteotomy tools can be solved; knee joints required to be subjected to osteotomy are subjected to osteotomy at 90-degree flexed positions in osteotomy procedures by the aid of the traditional osteotomy tools, but can be subjected to osteotomy at the 90-degree flexed positions by the osteotomy plate and also can be subjected to osteotomy at extension positions by the osteotomy plate, accordingly, lower extremity force lines can be measured while the knee joints are subjected to osteotomy, and the osteotomy accuracy can be improved.