Electric bicycle side pipe welding positioning device and positioning method

The electric bicycle side pipe welding positioning device comprises a positioning wall and pressing positioning mechanisms, the pressing positioning mechanisms are distributed on the side of a side pipe supporting seat on the positioning wall, and a side pipe assembly, clamped into the side pipe supporting seat, of an electric bicycle is pressed and positioned on the wall face of the positioning wall through the pressing positioning mechanisms; the pressing and positioning mechanism comprises a rotating seat, an extending arm and a pressing plate, and the pressing plate adjusts the pressing and positioning direction relative to the side pipe assembly through rotation of the rotating seat and extension of the extending arm; the extension arm comprises a first telescopic arm, a second telescopic arm and an air pressure type telescopic arm which are connected in sequence, and the air pressure type telescopic arm connected with the pressing plate is provided with an air pressure cavity; under the state that the p