The influence mechanism of the internal stress in quartz on the precision of digital sun sensors is theoretically investigated. The stress birefringence test of quartz specimens is conducted and the different quartz specimens are mounted on the digital sun sensors for a full visual field test. The means to control the stress level of quartz materials are put forwards. The research results show that there exists interference spots only for the quartz specimens with locally concentrated internal stresses, which is consistent with the theoretical analysis result.