A method of multiple-objective optimization is proposed for parameter designing of laser die-surface hardening. The mechanical properties (wear resistance and hardness) and the geometrical properties (hardening depth and surface roughness), which control the hardening effect, are taken as the optimization objectives. A regression analysis is applied to build a non-linear equation for mapping the hardening parameters to the optimization objectives. Multiple constraints are analysed and a model of non-linear multi-objectives is established to optimize the parameters of laser die-surface hardening. The particle swarm optimization (PSO) technique is used for solving this optimization problem. The objectives are contradictive, since the laser die-surface hardening increases the surface hardness of the die, but increases the surface roughness as well. To overcome this problem, the surface roughness is set not only as an objective, but also as a constraint, so that a special fitness function is designed for the iteration of the optimal solution. The die of an auto body is used as an example to test the optimization of parameters. The optimization results show that the optimal parameters can be obtained using this method for laser die-surface hardening which satisfy the hardening requirement, and reduce the hardening time and cost.