Abstract: This paper introduces the structure and the working principle of a magnetic unit used on tracked wall-climbing robot.An FEM(finite element method) numerical model of the single unit is developed,and the magnetic field results under different working conditions are solved by ANSYS software.Through a series of measurements on the output torque of the driving motor,we present a planar force equation of the track,which provides a base for the dynamics and the kinematics of the robot.