A novel two-ring-resonantor in parallel combined Rayleigh backscattering fiber optic gyroscope (RBFOG) is proposed based on the single ring scheme. The theoretical model of the two-ring combined RBFOG is established by using two 2×2 fiber star coupler. The expression of detection signal intensity is deduced. The output signal characteristics are analyzed by optimizing the structure parameters of the two-ring cavity lengths and coupling ratios. The experimental system is constructed with cavity lengths of 1500 m and 1078 m at coupling ratios of 95.23% and 94.88% respectively. Rayleigh backscattering signals are measured at different rotation rate by OTDR. Feasibility of the novel structure is validated. Compared with single-ring RBFOG, the two-ring system increases measuring effective data, and is propitious to recognize, and the measuring precision is improved.