OBJECTIVE To optimize the extraction process of polysaccharides from Dendrobium officinale， and preliminarily study its effect on acute lung injury （ALI） in mice. METHODS Using D. officinale as raw material， the polysaccharides were extracted from D. officinale by ultrasonic-assisted hot water immersion. Using the extraction rate of D. officinale polysaccharides as response value， the single-factor experiments and Box-Behnken response surface method were used to optimize the ratio of material to liquid， extraction time and extraction temperature. ALI mice were induced by lipopolysaccharide. Using prednisone acetate （5 mg/kg） as the positive control， the effects on the mass ratio of wet and dry lung and pathological changes of lung tissue （HE staining and Masson staining） of low-dose， medium-dose and high-dose D. officinale polysaccharides （50，100，200 mg/kg） were investigated. RESULTS The optimal extraction technology of D. officinale polysaccharides was as follows： the ratio of material to liquid was 1∶25 （g/mL）， the extracting time was 1 h， and the extracting temperature was 58 ℃ . Under these conditions， the average extraction rate of D. officinale polysaccharides was 37.75% （RSD＝1.12%，n＝3）， the relative error of which with predicted value （38.63%） was 2.28%. Compared with the model group， the ratios of wet and dry lung in the positive control group and D. officinale polysaccharides groups were all decreased significantly （P＜0.05 or P＜0.01）， and the pathological changes in lung tissue （severe destruction of alveolar structure， significant widening of alveolar septa， extensive infiltration of inflammatory cells and proliferation of fibroblasts） were alleviated to varying degrees. CONCLUSIONS The optimal extraction process of D. officinale polysaccharides is feasible； the obtained polysaccharide extract has a certain improvement effect on ALI in mice.