Abstract: Objective:The purposes of this study were to estimated the probability of ACL injury using stochastic biomechanical model as an attempt to understand the effect of skill level and gender on ACL injuries and risk factors during sidestep cutting task.Method:Kinematic,kinetic and EMG data were collected for both basketball players and non-athlete college students during sidestep cutting task.Monte Carlo Simulation was used to obtain the data of ACL injury and biomechanical characteristics of simulated jumps.The risk factors of ACL injuries were indentified by paired t-test to compare the difference of biomechanical characteristics between injury and non-injury jumps.Two-way ANOVA was used to identify the effect of skill level and gender on ACL injuries.Resuts:The simulated female-to-male injury rate ratios for basketball players and non-athletes were 18.36 and 13.04.Except gastrocnemius force of male basketball players and normal college students(P=0.553,P=0.773),internal rotation moment for female basketball players(P =0.981),vertical ground reaction force of male college students(P=0.81),the other paremeters showed significant differences between simulated injury trials than non-injury jumps(P<0.05).Besides,the distance of COP to ankle(P =0.114),sagittal plane loading(P=0.061)and non-sagittal plane loading(P=0.58)had no interaction between gender and skill levels,the others had significant interaction(P<0.01).Conclusion:Both the skill levels and gender effect ACL injuries and they have the interaciton effect.The females and basketball players have higher risk of ACL injuries than males and college students with no trainning experience.