The vehicle performances are studied through the ride comfort and handling stability commonly. While the lateral performance should be mainly considered for the centre axle trailer combination, such as the maximum stable side-inclination, the anti-rolling stability, the lateral stability and so on. Based on the finite element method, a rigid-flexible coupling model for the truck combination was built and analyzed in the multi-body environment (ADAMS), in which the key components of the chassis and cab suspension were treated as flexible bodies. According to the auto standards and regulations, the lateral stability of the centre axle trailer was evaluated through several simulation analyses. The variables' effects on the lateral stability were studied by design of experiment. Furthermore, in order to improve the lateral stability of the trailer combination, the optimal design was obtained by the co-simulation of the ADAMS/Car, iSIGHT and Matlab.