Abstract: 25Cr3MoA steel was treated using different quenching temperatures and 600 ℃ tempering before the nitriding treatment. Then, the vacuum pulse gas nitriding tests were conducted on the 25Cr3MoA steel after the different quenching and tempering treatments. The microstructure, surface hardness, and the hardness gradient and brittleness of the nitrided layer were studied. The results show that the lath martensite and retained austenite structure of 25Cr3MoA steel after quenching at different temperatures became coarser with the increase of quenching temperature, and the coarsening temperature is 950 ℃. As the quenching temperature raised, the thickness of white bright layer of nitrided 25Cr3MoA steel increased, and the microstructure of nitrided layer became coarser. When the quenching temperature is 900 ℃, the thickness of the white bright layer is about 10~15 μm. At this condition, the grain size of nitrided layer is small, and its microstructure is relatively uniform. Also, the nitrided layer depth increased with the rise of quenching temperature, and the microstructure of the nitrided layer became significantly coarser. Based on the comprehensive analyses results of the microstructure, structure, and properties of the nitrided layer with different quenching temperatures, it can be concluded that 900 ℃ is a proper quenching temperature for 25Cr3MoA steel before nitriding.