By analyzing the fault phenomenon of hydraulic locking circuit of a special vehicle in a large temperature difference environment,the calculation model was established and the test fixture was designed to verify .It is shown that in the environment of large temperature difference,the pressure change of fluid medium in the hydraulic locking circuit is obvious,which exceeds the maximum opening pressure of the two-way hydraulic lock when the temperature is rising,and the difference is large compared with the design value of the circuit.Finally,the measures to solve the fault under the condition of large temperature difference were put forward.The test proves that the method of increasing the hydraulic lock control ratio or manually reducing the oil pressure of the lock circuit can solve the fault.It provides certain reference for engineering design and application.