The invention relates to a fire box hidden door structure which comprises a U-type rotating shaft transmission device, two sector tri-petal type hinge devices and hyperbolic door guiding and limiting devices. The two sector tri-petal type hinge devices are arranged on the two sides of the U-type rotating shaft transmission device through a rotating shaft respectively to achieve eccentric moving and hyperbolic opening of a door. The hyperbolic door guiding and limiting devices comprise two wedge-shaped fixing blocks, wherein one hyperbolic door guiding and limiting device is fixed between the fire box hidden door and the rotating shaft, the hyperbolic door guiding and limiting device stops rotating when the door is opened to 180 degrees for the second time, and the other hyperbolic door guiding and limiting device is fixed inside the U-type rotating shaft transmission device to control a door leaf not to collide with an outer fade facing when the door leaf is opened for the first time. The fire box hidden door structure widens the applied range of a fire box, eccentric moving and hyperbolic opening are achieved, and thus the door leaf can be opened to 180 degrees.