The structure

operating and the characteristics of emission and stability of beam current for field emission gun（FEG） are reported. Experimental measurements show that if the vacuum in the gun chamber is better than 6. 67×10-7 Pa and the field emission current is 0. 9μA

the stability of beam current is better than 5% in 10 minutes

and if the acceleration voltage is 40kV

the radius of the virtual source of FEG is smaller than l. 3 nm and the brightness of FEG is higher than 5×109 A/cm2. sr. The results show that it is a new FEG of high brightness with very small beam spot. It can be used in SEM

STEM and other electron probe systenis.