Abstract: The energy efficiency ratio of ultra-low temperature mixed refrigerant cryogenic system is low.The problems that high compressor exhaust temperature and pressure always exist.For the sake of improving the ultra-low temperature cryogenic performance and ensure its safe and reliable operation，constructing a five-element mixed refrigerant ultralow temperature test bed is essential.The method that combined operation of the expansion tank and the control valve on the performance was analyzed.The results show that the strategy can not only improve the system cooling rate，optimize the system running components，but also reduce the total power consumption of the compressor，control the exhaust pressure and temperature in the safe range.