The present invention discloses an automatic nucleic acid extractor applied to the technical field of biology to extract nucleic acid, and the purpose of the present invention is to resolve the problem that processes, such as nucleic acid extraction, purification, semi-quantitativework, etc., cannot be fulfilled in one step. The mechanical parts include reserve part plates, an X-axis bracket (18), a Y-axis bracket (24), a second Y-direction slide plate (27), a first Y-direction slide plate (28), etc. The X-axis bracket (18) is horizontally fixed over a workbench (1) by means of upright columns and beams. The Y-axis bracket (24) is fixed on an X-axis slide plate (21), a Y-axis supporting arm (25) is vertical to an X-axis supporting plate (19), the second Y-direction slide plate (27) and the first Y-direction slide plate (28) are firmly integrated together by means of the reinforcing plate (29) of the Y-axis supporting arm and are nested on the Y-axis supporting arm (25) in the form of matching sliding connection. The reserve part plates, a waste liquid plate, a box cover plate, a reagent plate, a dilution plate, reaction plates and metal baths are fixed on the workbench (1). Stepper motors are connected with electric control parts via wires.