Abstract: Effects of space environment upon fiber-optic gyroscope(FOG) performance were studied, and a new-style assemble of 3-axis fiber optic-gyroscope used in satellite was designed. Simulation experiment was finished to analyze the effects of space radiation, vacuum environment and temperature cycle upon FOG. And the main mechanism of the effects of space environment upon FOG was obtained by analyzing the experimental data. A bias error model was developed by using least squares filtering, and a scale factor error model was developed by using look-up table. Both models were implemented in field programmed gate array (FPGA) for compensation of bias stability, which reduces the bias stability to 0.1(°)/h. The reasons for dead band in space are analyzed, and the error of dead band is to be suppressed by using the cycle phase modulation. During the design of the fiber optic gyroscope, the technology of multiplexing and redundancy of the light source, and the protective measures in space as well as the fault diagnosis in orbit are designed and implemented.