OBJECTIVE： To study the decoction rate changes of 4 active ingredients in the volatile oil of Curcuma phaeocaulis before and after combined with Sparganium stoloniferum， and provide reference for showing the compatibility mechanism of C. phaeocaulis and S. stoloniferum. METHODS： HPLC was used to simultaneously determine the contents of 4 active ingredients （curdione， curcumol， germacrone and β-elemene） in the volatile oil of C. phaeocaulis after C. phaeocaulis single decoction and combined decoction with S. stoloniferum. And the fried rates of each ingredient were compared. RESULTS： Compared with C. phaeocaulis single decoction， there was significant difference in the fried amounts of curdione， curcumol， germacrone in the volatile oil after combined decoction （P＜0.05） and no significant difference in fried rate of β-elemene （P＞0.05）. CONCLUSIONS： The combined decoction of C. phaeocaulis and S. stoloniferum can effectively improve the dissolution of curdione， curcumol， germacrone in the volatile oil. It may be the reason for the enhancement of efficacy after compatibility.