Considering vehicles running in many different work conditions, the mathematical models of suspension, steering and braking system are established. The intercon nections and confinements among the three systems are analyzed. Based on the ana lysis of interrelationships among the systems operated under different work cond itions, the problems needed to be paid attention to and the measures needed to b e taken in the system designs are presented. The results of simulation and testi ng show the close connection and interaction among the three systems, and the co rrectness of the established models.