A photoelectric reference ruler is designed based on position sensitive detector (PSD) for providing the reference length. A calibration method of the photoelectric reference ruler is proposed, which introduces the common points for transition between the PSD coordinate systems. The common points are confirmed based on the special workpiece with positioning holes. Through placing the 1.5-in. ball target on the positioning holes, the coordinate systems and the common points for transformations are structured by high-precision measurement instruments. After the calibration, the double-theodolites system is oriented by the photoelectric reference ruler and operated to measure the spatial points and distances in the experiment. The mean error is <0.18  mm in points measurement and <0.14  mm in distance measurement, and the feasibility of the proposed calibration method is validated. Compared with the traditional reference ruler, the photoelectric reference ruler is proved to be applicable for measurement system orientation and spatial large-scale measurement.