The ABS (anti-lock braking system) relay valve is the key component of anti-lock braking system in most commercial
vehicles such as trucks, tractor-trailers, etc. In this paper, structure of ABS relay valve and its work theory were analyzed.
Then a mathematical model of ABS relay valve, which was investigated by dividing into electronic part, magnetic part,
pneumatic part and mechanical part, was set up. The displacement of spools and the response of pressure increasing,
holding, releasing of ABS relay valve were simulated and analyzed under conditions of control pressure 500 KPa,
braking pressure 600 KPa, atmospheric pressure 100 KPa and air temperature 310 K. Thisarticle provides reliable
theory for improving the performance and efficiency of anti-lock braking system of vehicles.