Abstract: Microwave assisted extraction (MAE) was used to extract emod in from Polygonum cuspidatum Sieb. et Zucc. The orthogonal test design was used to optmiize the effects of microwave power, particle size and extractiontmie on the extraction yield of emodin. Parallel tests were carried out including the optimal process, water extractionm ethod and ethanol refluxing method. The results showed that particle size of P. cuspidatum and microwave power are the significant factors with P< 0.01 and P< 0.05, respectively and time is an affective factor on the extraction of emod in( 0.05 < P < 0.1). Microwave assisted extraction method is superior to water extraction and ethanol refluxing method. With 70% a lcohol aqueous so lution, microwave power 480W for 20min, the yield of extraction of MAE was 1.63%.