The invention discloses a diagnosis system and method for a natural gas orifice plate flowmeter. The system comprises a diagnosis controller and a remote control terminal communicating with the diagnosis controller through a local area network. The diagnosis controller comprises a central control unit arranged on a printed circuit board, a check standard signal generator, a standard signal measurement module and a communication module. An input end of the check standard signal generator is electrically connected with the central control unit, an output end of the check standard signal generator is electrically connected with a signal circuit in a natural gas orifice plate flowmeter, and the check standard signal generator is used for providing a standard signal source for the signal circuit. An input end of the standard signal measurement module is electrically connected with a flow computer in the natural gas orifice plate flowmeter, an output end of the standard signal measurement module is electrically connected with the central control unit, and the standard signal measurement module is used for measuring a return signal obtained from the flow computer. The communication moduleis electrically connected with the central control unit and used for achieving communication between the central control unit and the flow computer, a secondary instrument in the natural gas orificeplate flowmeter and the remote control terminal.