Orthogonal test of supercritical carbon dioxide extraction was carried out to obtain optimum condition as follows: pressure 25MPa, temperature 45℃, time 100 minutes, flow rate of CO2 30kg/h. The yield of volatile oil 1.3163%. GC-MS was used to analyze the components and determine their content. It showed that the main components of volatile oil from Schizonepeta tenuifolia Briq. are pulegone and menthone. However, dihydrojasmone and terrein which had never been reported in surveyed literature have been identified. It was the first time to use two-step separation method to purify the volatile oil from Schizonepeta tenuifolia Briq.. The result showed that by using two-step method, the content of the unsaturated fat acid and its ester from Schizonepeta tenuifolia Briq. decreased effectively. It was also seen that the content of pulegone and menthone increased dramatically compared to one-step method. Therefore, two-step method is a good method for purifying volatile oil from Schizonepeta tenuifolia Briq.. It can be used in industries.