Asymmetric faults are one of the common fault modes in high-lift systems. If not detected in time, they will affect aircraft-level safety. In order to solve this problem, the maximum asymmetry angle of wing deflection and the hardest working condition of high-lift system are taken as constraints, and the method of calculating the detection threshold of system position asymmetry and velocity asymmetry is proposed. In the calculation process, the influence of various factors on the asymmetry angle during the detection and control of the maximum asymmetry value of the left and right side angle during the normal operation of the flap/slat is considered in multiple dimensions, including factors such as the clearance on the transmission line, stiffness, sensor accuracy, as well as the software detection time of control equipment and the braking time of the system. Based on the above calculation method, the measurement values of position asymmetry under certain parameters are calculated based on a high-lift system. Using the calculated asymmetric detection values, a simulation model of asymmetric monitoring of high lift system is constructed in Simulink environment, and the validity of the method is verified.