Printed-circuit-board ion trap (PCBIT) is a novel ion trap mass analyzer,which is capable of optimizing its internal electric field distributions by adjusting the radio frequency (RF) voltage-divided ratio to improve its analytical performance.This work introduced odd electric field components into the trapping volume to achieve unidirectional ion ejection by applying asymmetric RF voltages to x electrode pairs of PCBIT.In this case,the center of ion vibration was displaced away from the geometrical center of PCBIT and ions were ejected predominantly through one of x electrode pairs.The relationship between asymmetric voltage-divided ratio (AV) and internal electric field distributions was investigated by simulation software SIMION and AXSIM.At the same time,the ion trajectories and simulated mass spectrum peaks were calculated.The results showed that,for ions with m/z 609 Th,a mass resolution over 2500 and an ion unidirectional ejection efficiency of over 90％ were achieved in PCBIT with AV=20％ at an appropriate frequency of AC.Using this method,ion unidirectional ejection efficiency of PCBIT can be significantly improved while maintaining a high mass resolution,which makes the PCBIT more suitable for developing miniaturized mass spectrometer.