The invention relates to an improved high-temperature and high-pressure resistant manhole access door. A door cover and a door seat of the access door are not easy to deform at high temperature, and have good sealing property. The access door comprises the door cover, the door seat and a flange, and is characterized in that the inner cavity of the door cover is provided with a door cavity, the door cover and the cover seat are compacted and sealed by an eyelet bolt and a ring nut, and the door seat is made of heat-resistant austenite structural steel.