Abstract: OBJECTIVE To optimize the extraction process of oil in Laggera pterodonta(DC.) Benth by orthogonal design L₉(3⁴). And then analysis chemical constitutes in the Laggera pterodonta(DC.) Benth oil. METHODS The experiment was performed with the extraction amount of volatile oil as the index, and the volume of water, the time of immersion, the time of extraction as affecting factors. GC-MS method was used to analysis chemical constitutes in the Laggera pterodonta(DC.) Benth oil. RESULTS Optimized extraction process was as follows: the Laggera pterodonta(DC.) Benth was soaked in 10 times of water for 2 hours, then distilled for 8 hours. Twenty compounds were separated from the Laggera pterodonta(DC.) Benth oil and were identified. CONCLUSION The method is stable and practicable; α-copaene, β-selinene and 1,2,3,4,4a,5,6,7-octahydro- 4a,8-dimethyl-α-methylene-2-naphthaleneacetic acid were the main compounds of Laggera pterodonta (DC.) Benth oil, the amount of the three compounds can attain 34.63%.