Abstract: In Karamay Petrochemical Company, #45 transformer oil was taken as single sealing oil in hydraulic relief valve of product tank, and condensate water at liquid sealing bottom froze due to low temperature, which resulted in failure of hydraulic relief valve.To solve this problem, #—50 antifreezing solution was chosen as lower levels liquid sealing of hydraulic relief valve, and #45 transformer oil was chosen as upper liquid,which composed complex liquid sealing.The complex liquid sealing effectively prevented the condensate water at the bottom of hydraulic relief valve frOm freezing,and met the needs of hydraulic relief valve in safe operation at low temperature environment.In addition, the plug of the hydraulic relief valve was transformed into a short joint with one-way valve to effectively control flow rate of liquid, which increased safety and work efficiency in daily care.