The invention discloses a single-rail synchronous conveying mechanism, a conveying flow line and a workpiece conveying method. The single-rail synchronous conveying mechanism comprises a horizontal displacement device and a lifting device. The lifting device lifts the horizontal displacement device to move up and down. The horizontal displacement device comprises a frame connected with the lifting device, a drive device disposed on the frame and a linear slide rail for carrying workpieces. The drive device drives the linear slide rail to reciprocate on the frame. By the structure, an embedded transmission mechanism for controlling forced cycle production is disclosed. The single-rail synchronous conveying mechanism is simple in structure and low in cost, the free cycle of the traditional belt flow lines is broken through, and fast and accurate machining is achieved while conveying time is shortened.