The invention discloses a paper jam detection mechanism and a printer. The paper jam detection mechanism comprises a main body frame, a movable plate body, a processor, an infrared transmitter and an infrared receiver. The movable plate body is rotationally arranged on the main body frame so that paper can pass between the movable plate body and the main body frame. The infrared transmitter and the infrared receiver are connected with the processor so as to be used for detecting rotation of the movable plate body. When at least one part of the movable plate body is located between the infrared transmitter and the infrared receiver, the transmission path of an infrared signal sent by the infrared transmitter to the infrared receiver is blocked. When paper jam of the printer occurs, the movable plate body is jacked up by the paper, the signal received by the infrared receiver is the same as the sent signal, and at the moment, paper jam can be determined to occur. The paper jam detection mechanism is not affected by the using environment, and error detection of paper jam is avoided when the paper jam detection mechanism is exposed to sunlight or other light sources.