Abstract: A high precision digital readout system was developed for the Faraday cup array ion collector in the magnetic mass spectrometer, which digitized the output signal of the ion collector so as to analyze and diagnose the ion composition in the ion beam. This digital readout system was composed of front-end processing circuit and data acquisition module. The gate integrators were employed in the front-end processing circuit to convert weak charge signal of 418 channels into voltage signal. The voltage signal was digitized by the data acquisition module, and the data were uploaded to the remote master computer through the Ethernet interface. The readout system realizes the digitization of input charge with a range from 0.1 pC to 120 pC, and the non-linearity error is less than 1.95% (full scale). The field application and test results show that the digital readout system can meet the experimental requirements, and it can also be widely used for measuring the weak current or charge signal in nuclear physics experiment and accelerator system.