It was obtained experimentally that the fluctuation of the held emission current was increased as the anode was approached to the emitter, under a low level of the vacuum condition. It is numerically solved that the number of generated gas molecules and ions by electron stimulated desorption on the anode surface come to the emitter surface. Under ultrahigh vacuum, the number was not so different for the distance. On the other hand, under low level vacuum condition, the number was increased largely as the anode approached the emitter. So the fluctuation can be increased when the anode approaches the emitter under low level vacuum condition.