In view of the problems of the compound action incoherence,the slow opening speed,and the high oil temperature of the hydraulic system for HZY06 type grab loader which was used by construction unit, a new type of hydraulic system of central rotary grab loader was designed. In the system, loadsensitive variable displacement pump and loadsensitive multivalve were used, and a differential connection was set up in the bucket cylinder circuit to meet the design requirements such as the compound action coherence, small power loss and fast grab opening speed. In order to verify the rationality of the system, the AMESim software was used to simulate and analyze the variable swing linkage loop and the grab cylinder loop. The simulation results show that the composite action is continuous and the opening time of the grab is only 155 s.