Abstract: The effect of furnace pressure on the depth uniformity of small modulus gear root was studied during ionic nitriding.The results show that at low furnace pressure,the nitriding layer of tooth root is shallow,and continuous nitriding white layer can not be formed,and copper color deposition will occur when saturated copper sulfate solution is used to erode it.With the increase of furnace pressure,the depth of tooth root nitriding layer increased,and the surface nitriding white layer was continuous.When the furnace pressure increased to 680Pa,the depth of tooth root nitriding layer reached 87%of the depth of pitch layer,and the nitriding layer was uniform.