Disclosed are a dormant lock mechanism for controlling a closing lock in a civil defence door and a mounting method of the dormant lock mechanism. The dormant lock mechanism comprises a sheath and a shaft sleeve which are disposed in a door leaf; the section of a cavity in the shaft sleeve is round; the end of the right side of the sheath is connected to the outside of the end of the left side of the shaft sleeve in a sleeving mode; a dormant lock shaft and a closing lock shaft are arranged in a communicating cavity in sequence from left to right, and the communicating cavity is formed through sleeved connection of the sheath and the shaft sleeve; a rotary knob is disposed outside the dormant lock shaft and inside the sheath; the end of the left side of the rotary knob is exposed out of the sheath, the end of the right side of the rotary knob and the dormant lock shaft are in sleeved connection and fixed, and the exposed portion of the rotary knob is connected with a handle; the dormant lock shaft comprises a lock core fixing end and a closing lock shaft connecting end; and a combinator is disposed in the dormant lock shaft, and the external diameter of the combinator is matched with the internal diameter of the dormant lock shaft. The dormant lock mechanism for controlling the closing lock in the civil defence door and the mounting method of the dormant lock mechanism have the characteristics of being safe, practical and the like, are excellent in popularization and practical values and can produce good economic benefits after being widely applied and popularized.