Piston reciprocating dynamic seal is the core component of the piston pressure balancer. The traditional piston reciprocating seal is prone to crawling and leaking under deep sea pressure. Based on the traditional theory of hydraulic reciprocating sealing, a new type of tandem type combined reciprocating dynamic sealing structure was proposed,which uses rectangular straightthrough labyrinth seal as front seal and star seal as main seal.The effect of the labyrinth seal on the dissipation of fluid pressure was verified by finite element analysis and the initial compression rate of the star circle was determined. The study shows that the labyrinth seal has a significant dissipation effect on the fluid pressure and can create a favorable sealing condition for the main seal.The contact stress of the main seal is greater than the hydrostatic pressure,combined with the sealing judgment conditions,the overall performance of the new combination seal can be judged to meet the design requirements.