Abstract: Objective: Based on the inhibitory effect of bacillomycin D (BD) and chitosan (CTS) on Penicillium digitatum, the effect of BD and CTS combination on post-harvest disease control and freshness preservation of sugar oranges was investigated. Method: Sugar oranges as the research object, mold strains were screened in the moldy sugar oranges for identification, and the minimum inhibitory concentration and FIC index of BD and CTS against P. digitatum were determined by the checkerboard microdilution method. Finally, treated sugar oranges with BD and CTS were stored and preserved under the conditions of 28 ℃ and 90% relative humidity, and the changes of morbidity, weight loss, hardness, soluble solids, enzyme activity and other indicators were determined. Result: The isolated and purified fungus from the sugar orange was identified as P. digitatum and named P. digitatum strain L6. The minimum inhibitory concentrations of BD and CTS for P. digitatum were 42.19 and 62.5 mg/L, respectively, and the FIC index was 0.75, indicating that the inhibition of BD and CTS on P. digitatum was cumulative. The storage and preservation results showed that after 15 days of storage, the weight loss rates of BD, CTS, and BD+CTS treated sugar oranges were 0.99%, 1.62%, and 1.09%, respectively, which were 66.44%, 45.08%, and 63.05% lower compared to the control groups. In addition, the results of changes in titratable acidity, soluble solids, ascorbic acid, and plant-related enzyme activities also indicated that BD, CTS, and BD+CTS combination treatments had good preservation effects on sugar oranges, with the BD+CTS combination treatment group having the best results. Conclusion: Both BD and CTS had significant inhibition effect on P. digitatum, which could be used for storage and preservation of sugar orange to extend the shelf life. The combination of the two could not only enhance the preservation effect, but also the low price of CTS could reduce the use of BD and save the cost.