Abstract: This paper describes a micro-computer controlled method of measuring the power density distribution of EB by scanning the beam over a pinhole. This is a direct measurement for an EB. A DMA with 2 channels was used for the data-accessing of the measurer. With this technique, the data-accessing rate can run up to 400 kHz, when a micro-computer with 2 MHz clock and two A/D converters with 5 μs converting rate were used. After data-processing, the direct and easily analyzed power distribution figures of profile and "isohypse" can be obtained.The authors provide thus an accurate and effective method of assessing the EB gun, investigating the difference between the theoretical computation and the objective reality of the electron optical system and researching the process technology of EB.