The invention discloses a transmission control mechanism for retracting and expanding an adjusting piece, and belongs to the field of engine jet pipe design. The mechanism is installed on a cylinder of a jet pipe and used for adjusting the adjusting piece located inside the cylinder. The transmission control mechanism for retracting and expanding the adjusting piece comprises a support (1), a swing motor (2) and a connecting rod mechanism, wherein the support (1) is used for fixing the cylinder and the swing motor (2), the two ends of the swing motor (2) are each provided with a cam, the cams rotate along with rotation of the swing motor (2), the connecting rod mechanism is installed on the side face of the cylinder, one end of the connecting rod mechanism stretches into the cylinder and is connected with the adjusting piece, and the other end of the connecting rod mechanism and the cams of the swing motor (2) form a sliding pair. When swinging, the swing motor 2 generates acting force on the connecting rod mechanism to enable the connecting rod mechanism to swing, so that the adjusting piece 8 is driven to retract or expand, and the retracting and expanding effect of the adjusting piece is remarkable due to the simple structure.