Abstract: The partial degrade of Ulva polysaccharidewere carried out by sulfuric acid degradation，the target degradation rate was（50±3）%，the key effects on partial degrade of Ulva polysaccharide were discussed．Their partial degrade master technological conditions were optimized by the response surface method．The results showed the optimized partial degrade technological conditions of Ulva polysaccharide were as follows：the concentration of sulfuric acid solution was 0.30 mol/L，degradation temperature was 95℃，polysaccharide concentration of 0.70%，degradation time was 1.0 h．Under the optimal conditions，the dagradation rate of the Ulva polysaccharide was 50.94%．