NOVELTY - A microbial strain, in particular Issatchenkia orientalis (S-7), deposited under CCTCC NO. M206098, is new.    USE - The microbial strain and methods are useful for preparing hemicellulose hydrolysate biological detoxification seed liquid; and for processing synchronous detoxification and fermentation of hemicellulose hydrolysate for producing xylitol and ethanol (all claimed).    ADVANTAGE - Compared with traditional method, the invention has higher production efficiency and product quality.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are: (1) a preparation method of the microbial strain; (2) a preparation method of hemicellulose hydrolysate biological detoxification seed liquid using the microorganism strain comprising: (a) preparing culture medium comprising 50 g/L of glucose, 2 g/L of magnesium heptahydrate (MgSO4.7H2O), 4 g/L of dipotassium hydrogen phosphate (K2HPO4), 6 g/L of monopotassium phosphate (KH2PO4) and 5 g/L of yeast paste; (b), inoculating the slant culture medium of CCTCC NO: M206098 in liquid seed culture medium; the charging amount is 20% of volume of the shake flask; and (c) cultivating for 12-18 hours on a shaker at 27-30 degrees C at a rotating speed as 200 rotations per minute (rpm), to obtain seed liquid for detoxification; (3) a method for preparing xylitol using the microbial strain comprising: (a) vacuum concentrating the hemicellulose hydrolysate fermented and detoxified by CCTCC NO: M206098 until xylose concentration is about 150 g/L; adjusting pH to 6 by ammonia; and adding 5 g/L of yeast paste, to obtain the hemicellulose hydrolysate culture medium for xylose fermentation; (b) processing xylitol fermentation by a shake flask; the charging amount is 10%; and then inoculating seed liquor of Candida tropicalis, CCTCC NO: M205067 according to inoculating amount as 5 v/v% at speed as 200 rpm; and fermenting at 33 degrees C until the xylose is consumed; and (c) collecting the centrifuged and settled thallus and putting in fresh hemicellulose hydrolysate culture medium, and continuously process new cycle of xylitol fermentation; and centrifuging the supernatant to prepare xylitol; (4) a method for processing synchronous detoxification and fermentation of hemicellulose hydrolysate using the strain to produce xylitol comprising: (a) vacuum concentrating the hemicellulose hydrolysate until the xylose content is about 100-150 g/L; adjusting the pH to 3-7 by alkali (calcium hydroxide or ammonia water), centrifuging or filtering to remove the precipitate; adding 5 g/L of yeast paste, to obtain the hemicellulose hydrolysate culture medium; (b) getting cultivated CCTCC NO:M206098 seed liquid and mixing with CCTCC NO:M205067 with same volume; and then inoculating in the hemicellulose hydrolysate according to inoculating amount as 5 v/v%; cultivating the shake flask until the xylose is consumed; and (c) centrifuging the collected and settled yeast cell and putting in fresh culture medium, and continuously processing synchronous detoxification and fermentation, and cycling, until the yeast cell cannot be used; and (5) a method for processing synchronous detoxification and fermentation of hemicellulose hydrolysate using the strain to produce ethanol comprising: (a) vacuum concentrating the hemicellulose hydrolysate until the xylose content is about 100-150 g/L; adjusting the pH to 3-7 by alkali (calcium hydroxide or ammonia water), centrifuging or filtering to remove the precipitate; adding 5 g/L of yeast paste, to obtain the hemicellulose hydrolysate culture medium; (b) getting cultivated CCTCC NO:M206098 seed liquid and mixing with CICC 1770 seed liquid with same volume; and then inoculating in the hemicellulose hydrolysate according to inoculating amount as 5 v/v%; cultivating the shake flask until the xylose is consumed; (c) centrifuging the collected and settled yeast cell and putting in fresh culture medium, and continuously processing synchronous detoxification and fermentation, and cycling, until the yeast cell cannot be used; and (d) distilling, recycling and concentrating the ethanol in the supernatant.