Basing upon therequirements of the scanning synchronization controller system of the geo-stationarymeteorology satellite (GSMS) and the characteristics of the solar target, a prototype ofon-board high accuracy sun sensor (HASS) and a set of testing equipment of this HASS hasbeen developed. The designed sun sensor, which is used on the GSMS both for the scanningsynchronization controller and for the alignment guiding of cloud pictures at earthstations, has two pairs of slits and uses an equivalent detection method to generate ahigh accuracy sun pulse. It has realized a measuring accuracy of 0.46 microseconds (r.m.s)when the satellite rotates at a rate of 100 r/min in the sector meridian plane of thesatellite ranging from -29.5° to +29.5°. In addition, the sensor has the characteristicsof high reliability, real-time and low power consumption.