High-precision and high-resolution tidal models play a crucial role in the inversion of time-varying gravitational fields, but the published tidal models generally only provide the main tidal components. The fitting coefficient matrix for the secondary tidal components needs to be published by other institutions or calculated independently. This paper first derives the calculation formula for the linear fitting of secondary tidal components in tidal models based on the theory of admittance and tidal potential data. Then, taking the EOT11a, EOT20, and FES2014b tidal models as examples, we calculate the fitting coefficient matrices for the secondary tidal components of each tidal model, as well as the corresponding ocean tide perturbation forces for CHAMP, GRACE, and GOCE satellites for a period of 1 day. Finally, we select the FES2014b tidal model to invert the 120th-order time-varying gravitational field of GRACE-FO for January 2021. The precision and impact of the secondary tidal linear fitting method in this paper are analyzed from different perspectives. The results show that the differences between the fitting coefficient matrices of the three tidal models and the corresponding ocean tide perturbation forces for the three satellites calculated in this paper and the results from the ITSG can be neglected. Considering the secondary tides can improve the precision of gravity potential coefficients above the 40th order and reduce the north-south strip errors in the time-varying gravitational field. The method presented in this paper can provide a reference for independently calculating the impact of secondary tidal components.