Objective:To optimize the technology parameters of the oil from Hedyotis diffusa by SFE-CO2

and to analyze the extractive components by GC-MS. Method: The experiments were designed with the method of orthogonal experiment

and efficiency of essential oil was used as value standards. The effect of various parameters

i.e.

pressure

temperature and sample particle size on yield was investigated with an analytical-scale supercritical fluid extraction (SFE) system to find the optimal conditions. The extractive components were analyzed by GC-MS. The relative content in the essential oil was determined by area normalization. Result: The optimized conditions were as follows: pressure (25 MPa)

temperature (50 ℃) and a sample particle size of 20-40 mesh. The result of the extractive components showed that in addition to containing higher fatty acid and its esters

the oil from H. diffusa also contained a lot of steroidal compounds. Conclusion: The oil from H. diffusa by SFE-CO2 is steady and feasible. It is an accurate and rapid method to identify structure by using GC-MS combined with Kovats retention index.