A loaded tooth contact analysis model was developed to assess transmission error by incorporating profile errors in a helical gear pair. Profile errors for all teeth of both the pinion and wheel were measured, and the mean profile error was computed and integrated into the model. To validate the model, static transmission error (STE) was measured experimentally. The experimental results, particularly the peak-to-peak static transmission error (PPSTE) in relation to torque and tooth-meshing harmonics, demonstrated consistency with the simulation outcomes. Subsequently, the model was employed to investigate the impact of surface waviness (SW) on the STE, focusing on SW amplitude, spatial frequency, and initial phase. It was observed that both the amplitude and spatial frequency of the SW influenced the PPSTE and the harmonic characteristics of the transmission error, while the initial phase of the waviness had no significant effect.