Abstract: Polysaccharide was extracted from Haematococcus pluvialis residue after extraction of astaxanthin by ultrasonic treatment cooperated with hot water extraction. Operating parameters for hot water extraction of polysaccharide from Haematococcus pluvialis were optimized using an orthogonal array design. The best results were obtained after ultrasonic treatment at 400 W for 30 min at a solid- to- solvent ratio of 1∶ 25( g / m L),water bath temperature of 90 ℃ for 3 h.Under such conditions,the extraction yield of polysaccharides was 3.48%,which was approximately 27% higher than that obtained by hot water extraction alone. The results showed that ultrasonic treatment cooperated with hot water extraction was a potential effective way,and providing theoretical basis for in depth research of Haematococcus pluvialis polysaccharide and for the development and application of residue.