A fire door lock structure includes a stopper disposed at a door frame and a latch assembly disposed at a fire door, wherein the latch assembly comprises a lock base, a latch unit, a blocking member, a pair of male and female means and a linking set. The latch unit includes a latch bolt. The latch unit and the blocking member are swingably disposed at an accommodating slot of the lock base. The blocking member is fastened at the stopper by the pair of male and female means, wherein the male means comprises a fastener formed at the blocking member. In the locked state, the fastener of the male means can be fastened at the stopper to prevent the stopper from being unable to block the latch bolt caused by a deformed fire door or deformed door frame under a fire condition.