Experimented the effect of the factors of temperature, St concentration, catalyst amount and reaction time on hydrolysis of stevioside catalyzed by hydrochloric acid or sulfamic acid. The results showed that stevioside conversion was nearly 100% , a yield of steviol reached 83.6% and a yield of isosteviol reached 12.4% catalyzed by hydrochloric acid with the optimum conditions. With the sulfamic acid catalyst, a conversion of stevioside of 100% nearly, a yield of steviol of 81.5% and a yield of isosteviol of 11.7% were obtained with the optimum condition.