A testing platform of hydraulic system was built, and the experiments about fine adjusting the pressure of wheel cylinder was performed based on PWM technology. Controlling carrier wave frequency of PWM was confirmed, and the oil-entered valve of ABS was tested with PWM. The duty ratio scope of oil-entered valve of ABS in PWM controlling was asserted. The experienced model of pressure increasing speed of wheel cylinder in PWM controlling was established. At last, the experienced model was validated with the tests.