Tidal theory for a three-dimensional Earth model stipulates that non-hydrostatic pre-stress arises from the transition from a spherically-symmetrical model to an asymmetrical model when introducing asymmetrical density increments. The contribution of non-hydrostatic pre-stress on tidal gravity has been neglected in previous studies since the effects of density increments are assumed to be smaller than those of rheology parameter increments. This study for the first time presents expressions for calculating the effects of non-hydrostatic pre-stress on tidal gravity and develops the tidal theory for a three-dimensional Earth model. The expressions are verified with the simple ocean-land model after which the effects of non-hydrostatic pre-stress are calculated using the real Earth model GyPSuM. The results suggest that although the effects of non-hydrostatic pre-stress are less than those of seismic wave velocity disturbance, the contribution to final results is significant and should not be neglected. By considering the collective contributions of seismic wave velocity disturbance, density disturbance, and non-hydrostatic pre-stress, the global theoretical variation of M2 semidiurnal gravimetric factors is obtained, and varies from −0.16% to 0.09% compared to those in a layered Earth model. M2 gravimetric factors measured by superconducting gravimeters worldwide are collected and compared to the theoretical results of this study. Theoretical values generated by the three-dimensional tidal theory for 11 of 14 stations show an improved match to measurements compared to those of traditional theory, which further verifies the accuracy of the formulae presented by this study.