Due to low adsorption efficiency of magnetic adsorption unit（MAU） of crawler wall-climbing robot, the parameters analysis and structural optimization design are carried out based on DOE, RSM and sensitivity analysis method. The functional relationship between the parameters of the MAU and the magnetic force is obtained by the finite element simulation model, DOE and RSM. The sensitivity of parameters of the MAU to the magnetic adsorption force is determined by the sensitivity analysis. The length, the width, the height of the permanent magnet, the thickness of the yoke and the distance between the permanent magnet and the wall are selected as the design variables. After the optimized design, the adsorption efficiency of the MAU is increased from 2.029 7 to 3.938 1.