An automatic injection device comprises at least an injection unit (1). The said injection unit (1) is formed by sealing a cover plate layer (3) with hydrophilic surfaces and a microfluid layer (4). The said cover plate layer (3) is provided with at least two through holes (5). The said microfluid layer (4) is provided with a hollow-out hybridization chamber (7) and at least two hollow-out microfluid channels (6). One end of each channel (6) is connected with the hybridization chamber (7), and the other end is connected with a through hole (5) of the cover plate layer (3) respectively. Taking advantage of the hydrophilicity of the cover plate, the automatic injection device makes a solution automatically enter and fill the hybridization chamber (7) and the microfluid channels (6) by the driving force of liquid surface tension. The flow uniformity of sample solution in microarray chip is achieved by the structural design of the hybridization chamber (7) and the microfluid channels (6). The automatic injection device has advantages of simple manufacture, easy operation, high hybridization efficiency, low sample cost, and automatic quantificational injection.