The mass effect of protective medium on the yield of nanometer diamond was studied to improve the yield of ultrafine diamond. The protective medium was water and the double protective medium (solid-state and liquid medium) was applied in the experiment. The results show that the influence of water protective medium mass on the yield of UFD is notable, and the optimum mass of water given in the experiment is 8.8 L.The application of the double protective medium can further improve the yield of ultrafine diamond.