With the performance of micromechanical gyroscopes approaching navigation grade, the scale factor nonlinearity is gradually becoming the limitation for high-performance applications such as the satellite attitude measurement. Coupling errors caused by parasitic capacitance are the major sources of scale factor nonlinearity but are usually neglected. In this article, the parasitic-capacitance coupling errors are introduced into the traditional gyroscope model and the scale factor nonlinearity induced by the coupling errors has been analyzed theoretically. The analysis indicates that two parasitic-capacitance couples from sense excitation signal to drive or sense detection signal are the dominant causes of scale factor nonlinearity. Two measurements (i.e., the amplitude of driving excitation signal and axis tuning voltage) are used to realize the calibration of coupling errors with the least square method. The experiment is also carried out to verify this novel calibration method on a navigation-grade honeycomb disk resonator gyroscope. The experimental results demonstrate that the coupling errors have decreased by 87.5 and 44.5 times, respectively, after the error compensation and that the scale factor nonlinearity has been improved from 244.8 ppm to 29.00 ppm. Furthermore, this calibration method can be applied to other resonator gyroscopes with the similar structure and control scheme.