To provide mass spectrometry equipped with a protection method of ion detector.

The mass spectrometry system includes a mass filter, mass filter control, an ion detector, and a controller equipped with an ion detector protective module. This ion detector protective module monitors output signal of the ion detector, allowing the controller to hinder the ion detector from accepting any more ion of specific mass if accumulation of output signal obtained by acceptance of the specific mass ion exceeds threshold. When exceeding threshold, the protective module allows the controller to send out a signal to the mass filter control and change DC voltage, preventing ion from turning to the ion detector while remaining time of SIM. Performing integration long enough to determine correct measurements will maintain accuracy in high signal level. Since higher signal level may achieve accurate measuring, only short integration time is required.