Load system is an important device of hybrid excavator test bed. According to technical requirements of 6 tons hybrid excavator test bed, technique parameters of load system was analyzed and hydraulic load system design scheme based on relief valve was determined. Fundamental diagram of hydraulic load system was designed and working process of load system was introduced. Based on AMESim software, numerical simulation model of hydraulic load system was established. With simulation research, maximum load power and typical load power of load system were simulated. Simulation results show that the hydraulic load system can meet design requirements. Prototype of hydraulic load system was developed and load experiment tests were carried out. Experimental results show that the hydraulic load system can be used to develop hybrid excavator performance test.