To improve the stability of LDs and reduce the laser beam drift in long-distance measurement, a BPNN-PID-based dual-mirror laser-beam drift compensation method was proposed. Two four-quadrant photodetectors, which were placed at the near and far ends of the measurement position, were employed to measure the laser beam drifts. Two 2D precision-angle mirror mounts integrated with two piezoelectric actuators were used to adjust the propagation direction of the laser beam. A model relating the laser beam drift and the angular variation of the angle mirror mounts was established. The angular variation was then fed back with the proposed BPNN-PID method based on the output of the laser beam drift detector, from which the laser beam drift can be automatically compensated. It was verified that the signal stabilities of a laser measurement system that was used for measuring the straightness and angular errors of linear stages improved from ±9 μm and ±5″ without laser-beam drift compensation to ±3 μm and ±1.5″ with laser-beam drift compensation over 15 minutes.