Abstract: A linear ion trap mass spectrometer could be built by four printed circuit board (PCB) plates. And the performance of the PCB ion trap was simulated. There were some higher order multipoles produced besides quadrupole field insides the PCB IT. The performance of PCB IT-MS is affected by the field distributions and can be adjusted and optimized. More than 4 000 mass resolution at FWHM can be achieved when the RF power is set up properly. Also there are nearly 100% ion detection efficiency.