Abstract: According to the principle that the difference between the dielectric constant of steam turbine oil and water is large, and the mixed phase acts as a dielectric, the capacitance value will change significantly. Using coaxial cylindrical capacitors as test sensors, eight oil samples that meeted the specifications of the world's mainstream naval ship steam turbine oil products were selected. The capacitance method was used to study the influence of room temperature (18 ~ 24 ℃) and 54 ℃ on the water separation of oil samples. The oil samples with obvious changes in water separation were selected to analyze the microscopic morphology of the oil layer after water separation. The results showed that: 1) At 54 ℃, from the mixing of oil and water to the end of separation, the capacitance value-time curve had a higher degree of coincidence, and the uniform mixing of oil and water had good repeatability, showing better repeatability and stability than room temperature; 2) The water separation rate curve had good repeatability, which verified the reliability of the capacitance method to evaluate the water separation of steam turbine oil, and at the same temperature, the water separation rate and demulsification time were less affected by the water phase distribution and movement; 3) When determining the water content of steam turbine oil by capacitance method, the ambient temperature was 54 ℃; 4) The analysis of the action mechanism showed that temperature was a key indicator that affected the water separation of the steam turbine oil.