The invention discloses a hydrodynamic force measuring system of an underwater vehicle. The hydrodynamic force measuring system comprises an anti-cavitation tail support key (2), an underwater vehicle front body (3), a tail force measuring six-component balance (4), a front body force measuring six-component balance (5), a soft brush (6), a sealing part (7), an inside-underwater-vehicle balance support (8), a front body balance support rod (9) and a tail balance support rod (10). The tail force measuring six-component balance (4) is in the shape of the tail of the underwater vehicle, thereby being capable of serving as the tail of the underwater vehicle and measuring hydrodynamic force on the tail of the underwater vehicle, stress on the underwater vehicle front body is transmitted to the front body force measuring six-component balance through the support in the balance, hydrodynamic force of the underwater vehicle front body is directly measured through the front body six-component balance, and the joint of the tail of the underwater vehicle and the front body is sealed by the sealing part and the soft brush. The hydrodynamic force measuring system can accurately measure the hydrodynamic force of the underwater vehicle front body and the tail in a separated type, and influence on measuring caused by hydrodynamic fluctuation of the tail is reduced.