Abstract: In this paper HP9845 microcomputer is applied to MAT261 mass spectrometer and software work about real time measuring and controlling procedure by means of ion counting method is reported.MAT261 mass spectrometer controlled by HP9845 realizes full-automation. Its scanning way is fixed-point may, and using integral method take average effect. In this way, we have obtained the result of low sensitivity, but it is unfavourable to measure small samples under low counting. Therefore, based on the former procedure NINT10, we built counting channel and ompile counting method procedure NINT21 by which taking pulse counting give rise to the sengitivity. The characteristic, structure, parameter, variability and application of numerical group of NINT21 procedure are described. The main procedure design, data acquisition and processing, the application of the procedure, and the comparison of the measured data about standard uran/um samples with standard value are discussed.