The calibration of the bias of on orbit HRG was researched with two proposed methods: calculation with orbit and Kalman filter. When the attitude directing was fixed, calculation with orbit could be adopted. When accurate mathematic model was known, Kalman filter could be adopted. Calculation with orbit needs less condition and was more operable, but calibration precision was worse than Kalman filter. The precision of calculation with orbit could be improved by filtering. The fact proved the feasibilities of the two methods.