In this paper, a specialized instrument of measuring inclination and deflection is proposed, which is developed by adopting photoelectric detection technique combined with design technique of precision instrument. This instrument adopts one-dimensional position sensitive detector PSD as the sensor of position, using simple pendulum structure to measure the inclination between a surface being measured and the earth's core. the measuring principle, structural design of the instrument has been introduced. It makes emphasis on the application research of the position sensitive detector PSD based on photoelectric transform, the research of high-accuracy data acquisition and processing technique, the linearization calibration method of PSD, etc. The measurement result can be shown directly on liquid crystal display, at the same time, for being convenient to communicate with the computer, the instrument also can send measurement data by infrared transmission and the computer can gather the data by the same means. This clinometer is of simple structure, high response speed , high measuring accuracy, strong interference rejection ability , low consumption , high characteristic of performance-cost ratio.