Abstract: The novel Mini-TOFMS developed in Tsinghua university not only has a large mass range and a high analysis speed,but also realized good resolution in a small volume.A detection system plays an important role in the performance of TOFMS.There exist simultaneous ion arrival and dead time effects in the time-to-digital converter,which is used in the detection system.These effects cause data loss and spectrum distortion at high detection rate and greatly limit the linear range of the spectrometer.This paper discusses simultaneous ion arrival and dead time effects in detail,and gives an effective correction method to eliminate the bad influence caused by the two effects.After the correction,both the precision and the linear range of the sprectrometer were largely improved.The result is satisfactory.