The invention discloses a nodular cast iron pipe die which comprises a supporting base, a first annular guide rail and a cast iron pipe die body. The first annular guide rail is connected to the supporting base, the cast iron pipe die is horizontally inserted into the first annular guide rail in a penetrating mode, and the rear end of the cast iron pipe die is rotationally connected into the first annular guide rail. A rotating speed reduction preventing mechanism is connected between the cast iron pipe die and the supporting base. When the rotating speed of the cast iron pipe die driven by the main driving motor is reduced, the centrifugal force is reduced, so that the main magnet block slides back under the action of resilience force of the first connecting spring, the adsorbed iron sliding block is pulled to be separated from the auxiliary magnet block and extruded to the pressure sensing switch, then the position of the auxiliary driving motor is fixed, and after the auxiliary driving motor is started, the pressure sensing switch is pressed to the pressure sensing switch. The auxiliary driving gear drives the cast iron pipe die to continuously rotate at a certain rotating speed, rotating speed recovery and centrifugal force recovery are achieved, and cast iron pipe manufacturing can be continuously carried out conveniently.