This work investigates the combination of two partially overlapping oscillating fields, aiming to analyze the effect of the separation distance between the fields on the production of electron-positron pairs in a vacuum. The process is simulated using computational quantum field theory (CQFT) method and the split-operator technique, which is based on the spacetime-dependent Dirac equation. The main focus is to analyze the influence of separation distance and frequency combination on the pairwise production rate and energy spectrum.The research results show that partially overlapping sub-critical oscillating fields can still effectively generate electron-positron pairs at small separation distances. The variation in separation distance along the overlapping direction significantly affects the pairwise production rate. For two oscillating fields with a fixed sum of frequencies, the separation distance has a notable effect on the pairwise production rate, with different frequency combinations exhibiting varying degrees of dependency.Further analysis of the energy spectrum reveals that the number and positions of spectral peaks are differently affected by the separation distance. Models with smaller frequency differences exhibit more concentrated energy distributions, generally presenting a single-peak structure. In contrast, models with larger frequency differences show more dispersed energy distributions, typically presenting a dual-peak structure. As the separation distance increases, the energy spectrum structure varies with different frequency combinations, especially for larger separation distances. In the case of larger frequency difference, the high-energy peak declines rapidly with separation distance increasing, leading to a lower proportion of high-energy electrons, while in the case of smaller frequency difference the change is relatively small. This phenomenon is further analyzed using energy transition probability distribution diagrams of particles.By analyzing the probability distribution diagrams of particle energy transitions, we obtain a preliminary understanding of the differences in various frequency combinations with respect to separation distance, and explain the changes in energy spectrum structure from the perspective of multiphoton transitions. Additionally, a more detailed analysis of these diagrams based on the law of conservation of energy, enables us to extract particle production trends corresponding to various multiphoton transition effects. It is found that for the same frequency combination, the trends of second- and third-order effects with varying separation distances are different, with higher-order effects decaying more rapidly.By analyzing the variation of probability of multiphoton transitions in a combined field with separation distance, as well as the variation of the probability of multiphoton transitions in a single field, we conclude that when the separation distance is small, the combined fields with larger frequency differences have advantages in the generation of electron-positron pair. However, when the separation distance is large, the combined fields with smaller frequency differences begin to play an important role and exhibit better stability, owing to their inherent multiphoton effects. For different cases under the combined influence of two fields, we conduct a more in-depth analysis of the differences between different orders within the same frequency combination and between the same order transitions under different frequency combinations. By proposing hypotheses and conducting computational verification, it is found that under the same conditions, the trend of normalized overlapping photon numbers changing with separation distances is consistent with the trend of corresponding particle production numbers, providing a more convenient method for testing the trend of particle production under separation distance.This study not only enriches our understanding of the generation of vacuum electron-positron pairs in strong fields, but also provides theoretical guidance and reference for designing experimental devices for generating pairs.