An apparatus and method for controlling adaptive reclosing based on transient stability of a power transmission line are disclosed. The apparatus includes a power angle calculation unit, an integral square error (ISE) second-order differential calculation unit, a stability determination unit, and a disconnection signal generation unit. The power angle calculation unit acquires the instantaneous value of a power angle based on voltage and phase angle measurement signals. The ISE second-order differential calculation unit acquires the instantaneous value of the second-order differential of the ISE of the power angle. The stability determination unit determines whether a system is stable or unstable based on the transitions in the instantaneous value of the second-order differential of the ISE. The disconnection signal generation unit generates a first disconnection signal and a second disconnection signal adapted to open or reclose the circuit breaker at the leader end and the circuit breaker at the follower end.