The invention discloses a method and an automatic instrument device for enriching and extracting target cells and separating single cells by using a positive magnetic bead method and performing immunity and molecular biology identification and analysis on single cells. By the method and the instrument device, the on/off of a capture magnet and a release magnet is controlled by various methods to complete target cell searching, capturing, cleaning and releasing operation once or for multiple times, so that the target cell detection sensitivity and stability are improved. When the capture magnet searches and captures the target cells, the search line is circular, square, comb-shaped, S-shaped or U-shaped. In addition, the captured substances are filtered, most free micro magnetic beads are removed, the purity of the product is further improved and the product can be used as a good experimental material. By combining a special filter and the adsorption of the capture magnet, more than 95 percent of free micro magnetic beads can be effectively removed. Meanwhile, the types of the single cells are identified and biological characteristics of the single cells are analyzed by an immunofluorescence staining method and a method in molecular biology, and effective biological indexes are provided for clinical diagnosis and treatment of cancers.