Abstract: For the hydraulic system valve parts after carburizing size exceeds the problem, carried out the carburizing process program design, discussed the impact of different process programs on the size of the valve. Through the carburizing and strengthening heat treatment process specimen size change comparison, micro-metallographic organization analysis, internal oxidation evaluation, carburizing layer depth test, find out 12CrNi3A material carburizing heat treatment size change rule. The results show that: carburizing before tempering preparatory heat treatment, carburizing process with the furnace temperature reduction to 820 ℃ ~ 860 ℃ and holding 10 min ~ 30min out of the heating chamber in a protective atmosphere cooling, carburizing high temperature tempering, normalizing, quenching, ice cooling and tempering for the best heat treatment process plan, while thickening the dimensional chain design and optimization of the parts manufacturing process program to meet the depth of carburizing layer 0.3mm ~ 0.6mm and carburized surface hardness HRC60~63.3 requirements. This guides the improvement of spare parts manufacturing and processing technology and heat treatment process to ensure the qualified delivery of related products.