In carrying out a project of developing an astronomical satellite, a prototype of high precision prism sun sensor was designed and constructed. The principle of prism solar positoin measurement is proposed. By this principle and some methods such as energy balance measurement, compensation of the variation of irradiance etc., a high precision measurement of solar position is realizable. Asun sensor designed on this principle has a high resolution and precision in small view fields, a small size, a light weight and a long service life. According to the conclusion of a formal evaluation, such an instrument has a resolution of 1" and a precision of ±3" in a view field of ±70'. The entire system weighs 2.5 kg, requires 1 watt of power consumption.