A method of soft-sensing is put forward after the relation between spindle's power and load torque is analysed.The soft-sensing model based on BP neural network is built up,using the spindle's stator-voltage,stator-current,no load current and spindle speed as secondary variables.With an example of aviation engine clutch bearing test-bed torque measurement,the simulation is done for the soft-sensing model.It is shown from the result that the proposed method can satisfy some given precision requirements.And a good method is provided to solve the difficulty of installing the valuable torque sensor.