Abstract: The coating formula was constituted by extracts of longan stones and pericarp，sodium benzoate， potassium sorbate and chitosan. This coating was applied in the semi-dried longan. Single factor and orthogonal experiments were used to optimize the coating formula. Results showed that the quality of semi-dried longan was mostly affected by sodium benzoate while the other three ingredients had no significant influence. Combined the preservation effects and costs，the coating formula was determined as follows：extracts of longan stones and pericarp at 26 Brix，with sodium benzoate concentration at 0.16%，potassium sorbate concentration at 1% and chitosan concentration at 1%.