According to the steering demand of four-way forklift truck, a kind of asymmetric steering mechanism (ASM) which is applicable to the four-way forklift truck was developed. In order to solve the steering performance deterioration in horizontal and longitudinal modes leaded by optimizing longitudinal and horizontal steering performances unilaterally and the disunion of optimization results data leaded by optimizing longitudinal and horizontal steering performances, the movement mathematics model of longitudinal four-wheel steering and horizontal two-wheel steering of ASM were established, respectively. The optimal mathematics model of longitudinal four-wheel steering and horizontal two-wheel steering were established. The asymmetry constraint of left and right steerings in the longitudinal four-wheel steering mode was put forward. Double objectives optimization functions aiming at approaching the Ackermann ideal steering performance were established. The Pareto-optimal solution set of ASM’s double objectives optimization functions was obtained by using the improved particle swarm optimization (PSO) algorithm. Finally, taking the non-dominated solution in the case that optimization results of steering performance were improved by 32.1% and 38.9% in the longitudinal and horizontal steering modes respectively as example, the proximity of steering performance in the longitudinal and horizontal steering modes to the Ackermann ideal steering performance and the rotation error of steering wheels were analyzed. The study provides theoretical reference for the optimization design of ASM.