Stevioside is a novel sweeter which is extracted from stevia leaves, and the 
stevioside in the stevia leaves mainly comprises two components of 
stevioside and 
rebaudioside A. The 
sweetness and 
mouthfeel of the 
rebaudioside A are both excellent, while the 
stevioside has certain lingering bitterness; and as the structure and nature of the 
rebaudioside A are approximate to the structure and nature of the stevioside, the separation of rebaudioside A and stevioside features high cost and great technical difficulty. In the invention, microorganisms are transformed for 20h-150h under the conditions that the concentration of the stevioside is 0.01%-5% (W / W), the temperature is 25-80 DEG C, the quantity of inverting 
enzyme or bacterial solution is 0.1%-10% (W / W), and the pH value is 2.0-7.0, and the stevioside contained in the rebaudioside A solution can be selectively degraded, thus obtaining high purity rebaudioside A containing no stevioside. The 
biotransformation method used in the invention has temperate conditions, does not use toxic 
methanol and other chemicals or 
macroporous resin with high cost, thus being a novel technology with safety, greenness and environmental friendliness.