The invention relates to a nuclear grade M-type pneumatic straight diaphragm valve which comprises a valve body, a diaphragm, a valve clack, a valve cover, a valve rod, an adjusting screw rod, a hand wheel rod, a hand wheel, an air cylinder, a support, an indicating rod and a guide plate. The valve body and the valve cover are connected to form space for containing the valve clack, the diaphragm is arranged on the connecting portion of the valve body and the valve cover, the lower end of the valve rod is connected with the valve clack, the upper end of the valve rod is connected with the adjusting screw rod, the upper end of the adjusting screw rod is connected with the hand wheel rod, the upper end of the hand wheel rod is connected with the hand wheel, the air cylinder is connected with the valve cover through the support, the upper end of the indicating rod is fixed on the guide plate, the lower end of the indicating rod is fixedly connected with the valve cover, and the guide plate is connected with the valve rod. Compared with the prior art, the nuclear grade M-type pneumatic straight diaphragm has the advantage of completely eradicating 'moving, disengaging, dripping and leaking' of a common valve.