A leveling system for a high-altitude operation platform by means of PWM (pulse-width modulation) control technology comprises a supporting arm, a control box, the high-altitude operation platform, an LEM (laser energy monitor) controller, a static angle sensor, a mercury angle switch, a connecting plate, an oil pump, an oil box, a power output device, a safety valve, a speed regulating valve, a leveling proportional valve, a two-way speed limiting valve and a leveling cylinder. The LEM controller is mounted on the operation platform, an analog circuit is controlled by the PWM control technology and digital output of a microprocessor, the LEM controller is used for detecting angles, outputting signals and controlling a proportion leveling valve, the oil pump, the speed regulating valve, the leveling proportional valve, the two-way speed limiting valve and the leveling cylinder to form a hydraulic oil circuit, and the leveling cylinder is organically connected with the supporting arm and the operation platform through connecting blocks. An inclined angle signal of the high-altitude operation platform can be constantly detected by a leveling controller, the inclined angle of a plane is automatically adjusted in the horizontal or vertical direction, and proportional quantities are automatically outputted, so that the operation platform is constantly kept horizontal.