The invention discloses an automatic pull wire sag controller comprising a motor base, a motor, a paddle, a guide shaft, a guide rod, a spring, an adapter male head, an adapter female head, a gear, a rack, a gear fixing bearing, a thrust bearing, a press plate and an eccentric clutch, wherein the left end of the guide shaft is inserted into a guide shaft mounting hole in the paddle, and connected with an output shaft of the motor; the left end of the guide rod is inserted into a guide rod mounting hole of the paddle; the eccentric clutch is arranged at the right end of the guide rod, and a clutch handle is arranged on the eccentric clutch; and the spring, the adapter male head, the adapter female head, the gear, the gear fixing bearing and the thrust bearing are sequentially sleeved on the guide shaft from left to right. According to the automatic pull wire sag controller provided by the invention, the wire is automatically taken up or paid off by controlling sag, so that nondeterminacy of manual control is avoided, automatic control is achieved, construction intensity is reduced, efficiency of electric wire stringing construction is improved, and security of electric wire stringing construction is ensured.