Addressing the issue of slot scheduling, this study employs a hierarchical allocating strategy and introduces the value of slot to construct a dual-objective optimizationmodel that balances fairness and efficiency.The validity of model is verified using historical data from a Level 3 airport in China. A comprehensive analysis of slot scheduling acrossdifferent levels, airlines, and date typesreveals the complexity of the process. Furthermore, the concept of overload allocation is introduced, and the offset evaluation criteria are redefined through the tolerance parameter, exploring the impact of optimal tolerance levels on slot scheduling. The results indicate that,compared to a single-objective model, the dual-objective model enhances fairness by only 0.30% and maximum slot displacement by 3.28%, while improving fairness by 26.00%. Moreover, the adjustment among airlines are more balanced, and historical requests are more likely to achieve fair allocation. Displacement on weekdays are observed to be lower than those on non-weekdays, exhibiting superior fairness(0.02%). Saturdays exhibit the highest displacement and the poorest fairness(1.11%). The optimal tolerance level is identified as 2 slots,which reduces overload allocation by 47.78%. This research provides novel insights into the slot scheduling and hold considerable reference value for airlines in the process of schedule.