An ion mobility spectrometer and method thereof are disclosed. The ion mobility spectrometer comprises an electrode and an ion source arranged adjacent to the electrode, wherein the ion mobility spectrometer further comprises: a single or a group of focusing guide electrodes arranged on the side of the ion source far away from the electrode and shaped as a funnel to output ions from the ion source; and a storage section arranged on the ion-outputting side of the focusing guide electrode for storing ions generated from the ion source. With the scheme of separating the ion source and the storage region, the present invention can facilitate exchange of different ion sources, so that a source can be replaced with another different source without any change in the subsequent configuration. The storage section can be made very thin in the direction of ion movement, its diameter can be very large, and the internal electric field is almost zero. Thus, it is possible to collect a huge amount of ions with a very small cluster thickness and a directional velocity of almost zero, leading to reduction in spread of ion mobility spectrum and increase in resolution.