Abstract: This paper established a clamping hydraulic system in two different color injection molding machines. The stabilities of different hydraulic systems were analyzed and optimized by means of experimental and simulating methods. The results indicated that, after a modification was performed up on the clamping hydraulic system of IA1600Ⅱbj new color injection molding machine, the mold positioning accuracy was improved from 1.87% to 0.67%. Moreover, the model repeatability also in-creased from 0.096% up to 0.052%, and the response time of new mold oil hydraulic insurance was shortened by 28%. The oil hydraulic safety performance of the updat-ed IA1600Ⅱbj new insurance clamping was improved significantly.