The invention discloses a resonator optical gyroscope based on resonant intracavity modulation. The resonator optical gyroscope comprises a light source, an isolator, a coupler C0, a coupler C1, a coupler C2, an inactive Y-branch coupler, a resonant cavity, a modulator, a first prober, a second prober, a first signal processing circuit, a second signal processing circuit and a modulation signal output circuit. The gyroscope provided by the invention uses the resonant intracavity modulation to replace an external two-circuit modulator structure, so that a gyroscope model is simplified and the integration degree of the gyroscope is greatly improved. The resonance characteristic of the resonant cavity provided by the invention enhances the modulation characteristic, so that a modulation voltage is reduced. Furthermore, the gyroscope provided by the invention is only provided with a modulation arm, however, a double modulation effect is achieved and the power consumption of the system is reduced. The modulation manner corresponding to the intracavity modulation provided by the invention uses a simple periodic square wave modulation curve, so that the non-linear error of the triangular wave is removed when being compared with the triangular wave modulation curve which is commonly used in external modulation; the asymmetry of a waveform is avoided; the gyroscope is beneficial to improvement on the entire precision of the gyroscope.