Abstract: To improve the performance of open-loop fiber-optical gyroscope (FOG), a mathematical model was presented to get its linear digital output. Based on this model, a digital interface was designed, which is a micro-control system consisting of gain control-able A/D converter and control software and able to auto-range and convert analog output to linear digital output. Experimental study was also made with an all polarization-maintain open-loop FOG. The results showed that, with using the above interface, the nonlinearity of FOG can be effectively reduced.