Abstract: The paper describes briefly the problems with the hydraulic system of the rotary heating furnace at the seamless steel division,Guangzhou I & S Co., Ltd. before the modification,and introduces the auto-pressure-relief unit and the enclosed hydraulic system designed and manufactured as Per relevant current Chinese specification in terms of configuration,drive principle and advantages,both are employed as the result of the modification. Relevant operational practice has shown that the said enclosed hydraulic system is capable of satisfactory operation and easy for adjustment/monitoring/maintenance,which results in a reduction of machine failuretate by 80%.The system is up the requirement for the production.