The Kuroshio turbine is a submersible power generator designed to be working against Kuroshio Current with an exclusively long system maintenance period. The long-term operational reliability of the shaft seal is one of the key factors in designing the Kuroshio turbine. Inspired by the ROV oil compensation system for thruster bearings and electrical junction boxes, a passive oil compensated shaft seal module, which is integrated with an oil compensator and shaft seals, is developed for a Floating Kuroshio Turbine (FKT). The passive oil compensator balances the surrounding seawater and the oil pressure, the internal spring evenly maintains the oil pressure slightly higher than the surrounding seawater to prevent water ingress. The new design of the passive oil compensated shaft seal module features high reliability, maintenance free and adaptability to any water depths, which will benefit and prolong FKT working endurance significantly. This study introduces different types of shaft seal and the concept of passive oil compensated shaft seal module. Then, a 1:25 scaled experimental model is established for several pressure tests and its performance is demonstrated.