Objective To compare the postoperative stability of unstable distal radius fractures fixed by locking screws with different length and analyze the stress distributions of distal screws and callus at different healing periods, so as to provide biomechanical references for choosing appropriate length of screws for treating distal radius fractures. Methods The three-dimensional finite element models of unstable distal radius fractures with fracture section and callus were established, respectively, and fixed by volar locking plates and locking screws with different length. Then different periods of fracture healing were simulated by assigning callus with different material properties. Stress distributions on callus and distal screws at different postoperative periods were analyzed, and compression stiffness of the whole fixation system was calculated according to the maximum axial displacement at fracture section. Results Under the same axial loads, the compression stiffness was basically the same by using unicortical screw with over 75% length or bi-cortical screw. With the screw length increasing, the maximum stress of callus was decreased gradually during the period of early healing; while the maximum stress of distal screws was increasing gradually with the increase of screw length at middle and last period of fracture healing, and the stress of distal bi-cortical screw was the largest. Conclusions Using the unicortical distal locking screws with at least 75% length can not only produce early stability， but also avoid extensor tendon injuries due to dorsal screw prominence.