Based on the technology of optical fiber, an analog sun sensor was designed. It consists of three parts: the optical head, optic-electronic sensor and the measurement and calculation of sun angle. The optical design of the sun sensor adopts two pairs of optical fiber and a central optical fiber, and then obtains the relative angular relationship between the sun and the spacecraft's own coordinate system by calculating the difference value of importing light of each pair of optical fiber. The optical structure can suit multi-fields of view, including both small and large. It can increase the accuracy of the positioning system. Optical fiber was used as a leader, which connected the optic-electronic sensor inside the spacecraft. Keeping the sensor deep inside the spacecraft will protect the sensor from being damaged by high-energy particle in space. Circuit and signal processing were briefly described, and compensation of the error was analyzed. Preliminary test has shown that the system accuracy can reach ±0.15 degrees. This sun sensor is particularly applicable to attitude control system of spacecraft and solar tracking system on ground.