This paper focuses on high-speed design of geometric parameters of any given target for Radar cross section (RCS) reduction. The Binary particle swarm op- timization (BPSO) and the Finite-di®erence time-domain (FDTD) method are combined to acquire a given object's optimum geometric parameters that would lead to its min- imal monostatic RCS. To promote the computation speed as well as the computation capacity in a further way, a par- allel FDTD code is imported in this paper. A basic strat- egy to reduce RCS of a canonical target is proposed. As an illustration of the ability of the optimizing method, the al- gorithm is applied to optimize the position and the width of the slot, which may reduce the monostatic RCS. To verify the e®ectiveness of the algorithm, all possible conditions in this problem are simulated and it is well shown that the optimizer could search out the minimal or subminimal solution quickly and e®ectively.