Abstract: Nitriding treatment was conducted on 40CrNiMoA steel crankshaft by using pit furnace gas nitriding process. Problems such as large consumption of ammonia,seriously aging of equipment and disqualification of product existed in the original nitriding process,so improvement was done. The resutls show that optimization measures such as lowering nitriding temperature,full pre-oxidation of the crankshaft,denitriding the equipment on a regular basis and control ammonia flow were adopted. After Optimization,product quality and equipment utilization rate were both raised,and ammonia consumption was lowered,so the costs were dropped largely.