The present invention discloses a motor efficiency analysis method for motor inverter. The method can be performed via a real-time motor operation efficiency display device. Based on the measured primary current signal and the voltage provided by the driving device, the device can estimate related data, such as the real-time efficiency, rotational speed, torque and stator resistance, by means of several algorithms. Besides, the device is designed to be applied to most motors; therefore, users can manage the efficiency of all motors of the factory without the need to stop the machines or the manufacturing process.