Abstract： Objective To study the rap force produced by stimulator of bone stress on fracture ends of lower limbs in different positions and fixation methods, and to examine changing relationship of rap force in vitro with the stress at fracture ends. Methods Ten complete fresh lower limb specimens of 5 cadavers were used to establish models of femur fracture, tibia fracture and tibiofibular fracture in sequence. The specimens with various fracture positions were all fixed with external fixators and plates successively. Ten specimens of each group under two fixation methods over various fracture positions were observed. Pressure sensor was located on transverse fracture over midshaft of specimens and fracture ends. Stimulator of bone stress was used to rap the heel of specimen. Rap force produced by stimulator and the compressive stress at the fracture ends under two fixation methods over various fracture positions were recorded, and their correlation was analyzed. Results A liner correlation was observed between rap force (50～350N) and fracture end stress (all r=1.000, P=0.000). Under the same rap force, the fracture end stress under the same fixation method was as follows: tibiofibular group ＞ tibia group ＞ femur group (P＜0.05). As to fracture ends stress on the same position, external fixator group is bigger than plate group (P＜0.05). Conclusions Corresponding stress over fracture end appears when rap force was given after fracture fixation. It is advised to give corresponding rap force on individual fracture position and fixation method so as to promote healing.