In view of the problem of the braking system defects in the running process of the trackless rubbertired cart with WC5J explosionproof diesel engine which was used in coal mine driving, the main problem was that the braking reaction time was too long,and the braking delay time was 05~1 s. When emergency braking, the cart could not immediately slowed down, there was security risk. At the same time there was a problem that the driver’〖KG-*2〗s leg brake force was not proportional to the pedal angle. Through the analysis and improvement to the principle of the hydraulic braking system, after experimental verification, the cart braking effect is good and the security risks is eliminated.