The invention discloses a volt-ampere-characteristic-based on-line diagnostic method for the temperature of a hollow cathode emitter. With the method disclosed by the invention, the temperature of thehollow cathode in working can be obtained effectively; and the method is operated conveniently and the universality is high. The existing hollow cathode emitter temperature measuring method need expensive diagnosis equipment and is operated complicatedly and is not easy to realize. However, according to the volt-ampere-characteristic-based on-line diagnostic method, the measurement of the emittertemperature that is difficult to measure is transformed into resistance measurement of the heating filament of the hollow cathode; and conventional parameters like the voltage and current in a testing device are recorded and calculated, so that the emitter temperature is obtained conveniently. Compared with the existing method, the volt-ampere-characteristic-based on-line diagnostic method has advantages of being simple and effective and having high universality.