A door machine mechanism of the fireproof door comprises a force exerted end which is activated to roll a rotary axle and a loading end for receiving the weight of the door curtain. The rotary axle comprises an internal axle and two external axles. The force exerted end and the loading end are applied on the internal axle and the external axle respectively. The internal axle and the external axle are normally coupled via a clutch mechanism. A torsion spring brake mechanism is used to normally brake the rotary axle against the load of the loading end by changing the inner diameter of the torsion spring, or when the torsion spring brake mechanism is subjected to an external force from the force exerted end, the rotary axle is released. As such, the clutch mechanism is controlled to interrupt the coupling of the internal axle and the external axle in the event of the fire alarm such that the door curtain falls and shuts the fireproof door.