Liquid-jet hammer have been successfully used in oil and gas drilling production for its high penetration rate and unlimited drilling depth. However, the damage of the bi-stable fluidic amplifier caused by complex stress has limited the working life of the liquid-jet hammer. In order to improving the performance of the liquid-jet hammer, the distribution of stresses in the bi-stable fluidic amplifier was studied by computation and the optimized structures of the bi-stable fluidic amplifier were proposed. Computational study results show that the optimized bi-stable fluidic amplifier can reduce the maximum stress one order of magnitude to improve stress situation obviously with longer service life.