[Objective] This study aimed to investigate the effects of two pre-freezing methods (vacuum freezing and atmospheric pressure freezing) and two dipping methods (sucrose impregnation before pre-freezing and sucrose impregnation during freeze-drying) on the quality of freeze-dried apple slices. [Methods] The freeze-drying process was divided into six groups: vacuum pre-freezing without sucrose immersion (VFFD), atmospheric pre-freezing without sucrose immersion (CFFD), vacuum pre-freezing with sucrose immersion (BSVFFD), vacuum pre-freezing with sucrose immersion (MSVFFD), atmospheric pre-freezing with sucrose immersion (BSCFFD) and atmospheric pre-freezing with sucrose immersion (MSCFFD). The main quality indexes of freeze-dried apple slices in each group were analyzed. [Results] The color ΔL^* of the MSVFFD group samples is relatively lower, while Δa^* and ΔE are relatively higher, presenting a deep red color. Sucrose impregnation significantly increased the yield of freeze-dried samples, with the highest in the MSVFFD and MSCFFD groups, followed by the BSVFFD and BSCFFD groups, and the lowest in the two control groups of VFFD and CFFD (P<0.05). Sucrose impregnation significantly reduced the deformation rate of freeze-dried samples, and there was no significant difference among the deformation rates of the four groups with sucrose impregnation, but they were significantly lower than the two control groups of VFFD and CFFD (P<0.05). Sucrose impregnation significantly enhanced the puncture hardness and work of freeze-dried samples. The MSVFFD group had the highest hardness, while the two control groups of VFFD and CFFD had the lowest hardness. Besides, the hardness of the three groups with vacuum freezing treatment was higher than that of the three groups with atmospheric freezing treatment, and the hardness of MSVFFD and MSCFFD groups was significantly higher than that of BSVFFD and BSCFFD groups, respectively (P<0.05). The dried samples of MSVFFD and MSCFFD groups had the lowest moisture absorption rate, while CFFD group had a significantly higher moisture absorption rate than the other groups (P<0.05). [Conclusion] The methods of vacuum freezing and sucrose impregnation during freeze-drying are more helpful in improving the quality of freeze-dried apple slices, and the MSVFFD group endows freeze-dried products with better overall quality.