The invention provides a preparation method for kansui root, comprising the following steps: kansui root is taken; rice vinegar with 30-40% of the weight of kansui root is added; the mixture is placed in a sealed container for covered moistening for 20-30 minutes; the kansui root which is subjected to covered moistening is placed in a microwave oven; the microwave output power is set to be 600-800 watts and the time is set to be 5-15 minutes; then the kansui root is taken out and the processed product of vinegar kansui root is obtained. The preparation method is simple and convenient in operation, can obviously shorten processing time and lead the preparation process to be easy to control. In addition, the toxicity of the obtained processed product of kansui root is decreased while the pharmacologic action is relatively strengthened.