In this paper, the birefringence sun sensor which based on birefringence of uniaxial crystal is proposed for the first time. There are two exit rays when the sunlight passes through the birefringence sun sensor. By calculating the coordinates of two exit rays on the APS surface, not only the pitch and yaw information but also roll information of the sun sensor relative to the sun are obtained. The designed optical system is composed of an APS CMOS image sensor, a pinhole imaging system and calcite. On the basis of Huygens' theory, a digital sun sensor imaging model combining pinhole imaging with uniaxial crystal was constructed. Based on the birefringence theory of uniaxial crystal, an optical system simulation model was established on computer. The parameters of aperture, uniaxial crystal size and spacing between optical axis and uniaxial crystal were designed, and the numerical simulation was carried out. The results indicate that the uniaxial crystal sun sensor with birefringence can realize the threedimensional measurement of the attitude, and has the characteristics of high precision and large field of view. © 2018 KASHYAP.