Abstract: 篢he papar has systematically discussed the digit circuits of MAT isotopic mass spectrometer in details. It was divided four parts: interface and data collectors,system controller,DAC-16 magnet fieId controller,other parts (include test borad and other devices ). It is usefuI for the users of MAT isotopic mass spectrometer, when there are some wrongs in the digit circuits,especially when they want to modify the software or hardware of the instruments。