Flat type differential ion mobility spectrometer capable of selectively detecting positive and negative ions

The invention discloses a flat type differential ion mobility spectrometer capable of selectively detecting positive and negative ions. The flat type differential ion mobility spectrometer comprises a positive and negative ion separating area, an ion migration area and a detecting area. The positive and negative ion separating area is composed of two groups of parallel electrode couples or parallel grids, and a certain voltage different is exerted on the parallel electrode couples or grids. Simply by changing the directions of the electric field between the two groups of electrode couples, the space separation of positive ions and negative ions can be achieved, and further the positive ions and the negative ions can be selectively imported into the migration area and the detecting area. Therefore, recombination of the positive ions and the negative ions due to mutual attraction can be avoided, and the detecting sensitivity can be enhanced.