For the high-precision positioning and orientation system, its zero-speed correction positioning accuracy is affected by the abnormal change of horizontal gravity in the driving route. The influence of horizontal gravity anomaly on the positioning error of positioning and orientation system is analyzed theoretically from the aspects of inertial navigation error mechanism and zero speed correction principle, and its error transfer formula is obtained. In order to verify the accuracy of the error transfer formula, the physical verification was carried out in the gravity anomaly test area, and the influence mechanism of horizontal gravity anomaly on the positioning accuracy of the positioning and orientation system wasverified. Throughgravityanomalycompensation, thehorizontalpositioning errorinthegravityanomaly areawasless than1m.Itputsforwardanewideaforfurtherimprovingthepositioningaccuracyofthepositioningandorientationsystem inthefuture.