Conditions of the extraction and purification of polysaccharides from suspension-cultured protocorms of Dendrobium candidum were optimized by orthogonal experiment.The results showed that the optimum technology of isolation is to extract about 3 times and 2 hours each time in 20 times water at 80℃,to precipitate polysaccharides with 80% ethanol,and to remove proteins when chloroform/n-butanol is 1∶0.4,the sample/ chloroform-n-butanol is 1∶0.35 and the abstracting time is 5 min.