The invention discloses an articular surface retaining type extendable tibial neoplasm knee joint prosthesis. The prosthesis comprises a steel plate type tibia proximal prosthesis, a patellar ligament fixing plate, an adjustable backbone extending joint, an adjusting nut, an adjustable medullary cavity extending handle and a fixing assembly; the steel plate type tibia proximal prosthesis is provided with a groove with a bone trabecula porous structure, the patellar ligament fixing plate is arranged in the groove with the bone trabecula porous structure, the adjustable backbone extending joint is arranged on the lower portion of the steel plate type tibia proximal prosthesis, the lower portion of the adjustable backbone extending joint is provided with a lower tibia segment, the adjustable medullary cavity extending handle is arranged on the lower tibia segment, and the lower tibia segment is fixed to the adjustable backbone extending joint in a matched mode through the adjustable medullary cavity extending handle. According to the articular surface retaining type extendable tibial neoplasm knee joint prosthesis, a bone growth function of a child patient can be guaranteed while a knee joint movement function is retained; in addition, the end face, closely attached to the osteoepiphysis, of the steel plate type tibia proximal prosthesis is provided with the bone trabecula porous structure, therefore, bone growth is promoted, a long-term biological fixation effect is formed, and the service life of the prosthesis is prolonged.