Automatic injection pen and injection method thereof

The invention discloses an automatic injection pen and an injection method thereof.The automatic injection pen comprises an injection mechanism, the injection mechanism comprises a tube and an injection head, the injection head is installed at the lower end of the tube, and the injection head is fixedly connected with the tube in a sealed mode; the operation shell comprises a main shell body and shaft sleeves, the main shell body is fixedly installed on the outer side face of the bobbin, the shaft sleeves are arranged at the upper end and the lower end of the main shell body, and the shaft sleeves and the main shell body are integrally formed. The bending frame is mounted in the bobbin, so that the sealing plug is conveniently driven to stably perform sliding injection through sliding of the bending frame, and meanwhile, the bending frame is connected with a threaded rod on the driving mechanism in a matched manner through a threaded sleeve; in this way, the lifting sliding and sliding speed of the sealing pl