In summer of 2008, green tides broke out in south Yellow Sea.First,the nutrition of floating algae was analyzed and then the algae were treated by sulphuric acid for getting reducing sugar. The effects of temperature(℃), treating time(min), sulphuric acid concentration(%), ratio of mass weight(%)on the biomass hydrolyzation were studied and the hydrolysis conditions were optimized by orthogonal analysis. The results showed that optimum conditions for floating Ulva prolifera biomass hydrolysis by sulphuric acid were 90 ℃ of treating temperature, 70 min of treating time, 5% of sulphuric acid concentration, 4.5% of ratio of the mass weight. Liquid chromatography analysis showed that the molar ratio of monosaccharides in hydrolyzate were glucose 1.71∶xylose 1.00∶rhamnose 1.29. Growth curves of five yeasts(IwSc1,S1,S2,1770,1766) were drawn in order to ferment the liquid at stationary phase.The results showed that S2 was the best for getting highest ethanol concentration with GC analysis. The ethanol concentration was 2.1 g/L and the ethanol conversion rate was 26%.Glucose concentration dropped from 18.26 g/L to 2.38 g/L and the utilization rate of it was 87%. S1, S2 and IwSc1 mainly use glucose compared with 1770,1766 which can use both glucose and xylose.