Abstract: A pierce-type electron gun with a plane LaB_6 cathode is described. This cathode has the advantages of the stable emission, anti-poisoning,simplicity and lower vacuum condition. At a pules acceleration anode voltage of 80 kV and cathode temperature of 1360℃, the focussed electron beam of 630mA can be obtained. Other experimental results of this gun are also discussed. This electron gun is used for standing-wave electron linac with 4 MeV energy.