The present invention relates to a method of improving detection sensitivity of an ion mobility spectrometer, comprising: inserting a sample into a sample receiving device of the ion mobility spectrometer; triggering an operation of spectra acquisition through an optocoupler; when the number of the acquired spectra reaches the level required to contain enough information for accurate detection of explosives with relatively high vapor pressure, adding a dopant instantly to the ionization region by controlling the ON/OFF-state of an electromagnetic valve; when the number of the acquired spectra reaches the level required to contain enough information for accurate detection of explosives with relatively low vapor pressure, stopping the acquisition operation, and turning off the electromagnetic valve so as to stop adding the dopant to the ionization region; analyzing all of the acquired spectra to obtain the detection result. The addition time of the dopant is controlled such that the dopant can take effect on the detection of some explosives with relatively low vapor pressure while the explosives which can be detected with higher sensitivity when no dopant is added can be analyzed in the case that the dopant concentration is very low, thereby achieving the optimal detection performance of the apparatus by taking account of its response to various explosives.