Abstract: The aim of this paper was to find the best chemical method to extract the soluble dietary fiber(SDF)from raspberry pomaces. Raspberry pomace SDF was extracted by acid and alkali methods,the effects of temperature,time,concentration of extractant(HCl or NaOH),and liquid-solid ratio on SDF extraction were studied,and the purity of SDF extract was determined. The purity of SDF extracts was determined by acid and alkali methods respectively,and the optimum chemical extraction method was preliminarily judged. Then Box-Behnken 4-factor 3-level response surface combination was used to optimize the extraction process. The results showed that the extraction rate of alkaline process was obviously higher than acid process,the yields of alkali and acid methods were 21.45%±2.3% and 3.39%±0.68% respectively,and the purity of SDF 73.84% and 76.17%,thus,alkaline process was better than acid process. The results of Box-Behnken of response surface experiment showed that the best alkaline extraction condition was 40℃,62 min,8.13 g/L NaOH and 25:1 liquid-solid ratio,and yield of SDF was 24.03%±1.01%. Overall,acid and alkaline process could be used to extract SDF from raspberry pomaces,but alkaline process was better;The best alkaline extraction condition acquired from Box-Behnken of response surface experiment could provide certain theoretical basis for rationalizing the by-products process of red raspberry.