Micropipette is a kind of precise liquid taking device (commonly known as gun) which can be adjusted at will within a certain capacity range. The basic principle is to rely on the up-down movement of piston in the device. The moving distance of gas piston is realized by the screw structure controlled by the adjusting wheel. The push button drives the push rod to make the piston move downward and eliminate the gas in the piston chamber. After loosening hands, the piston restores to its original position under the action of the reset spring, thus completing a suction process.