The invention relates to an automatic collecting device and a collecting method for shared bicycles. The automatic collecting device comprises a fixing seat, a rotatable lifting device, a horizontal length adjusting device, a vertical height adjusting device, a positioning, grasping and collating device and a control unit. The fixing seat is arranged at one side of a collecting platform; the rotatable lifting device comprises a first lifting oil cylinder and a first rotating head arranged at the end part of a piston rod of the first lifting oil cylinder; the horizontal length adjusting device comprises a first horizontal telescopic oil cylinder fixedly connected with the first rotating head and a first fixing head arranged at the end part of a piston rod of the first horizontal telescopic oil cylinder; the vertical height adjusting device comprises a second lifting oil cylinder fixedly connected with the first fixing head and a second rotating head arranged at the end part of a piston rod of the second lifting oil cylinder; and the positioning, grasping and collating device comprises a positioning photo comparison detection device, a grasping device and a collating device. The automatic collecting device provided by the invention has the characteristics of high work reliability, low cost and multiple functions.