Abstract: Water sealed tank is one of the key equipments for backfire protection of the flare system. Its overflow mode will produce the problems in condensed oil discharge, while skimming and water charge operations of the water sealed tanks also will affect the flare system. Typical water sealed tank structure and overflow mode are summarized and analyzed. The results show that the water sealed tank equipped with baffles can significantly reduce water volume used and the overflow port designed at the tank wall can effectively skim oil and avoid potential safety hazards during skimming. Through a case, structure and operating parameters of typical water sealed tank with tank wall openings are proposed and suggestion to design the location for overflow port of flare water sealed tank is provided. It is considered that opening at different heights of the water sealed tank should be be a priority in the design. If communicating pipe overflow mode is used, the detailed operating procedures for skimming and water changing should be formulated and strictly followed them.