Objective: To optimize preparation process of volatile oil from Houttuyniae Herba dropping pills. Method: Volatile oil from Houttuyniae Herba was extracted by supercritical CO2 fluid extraction.Taking overall desirability of appearance grade

dissolve time limit and methyl-n-nonyl-ketone content as dependent variable

on the basis of single factor tests

central composite design and response surface methodology was adopted optimize preparation technology with dropping distance

proportion of matrix and volatile oil

liquid temperature and upper temperature of condenser pipe as independent variables.The content of methyl-n-nonyl-ketone was determined by GC. Result: Optimum preparation technology was as follows:dropper caliber of 2 mm

dripping speed of 50 d·min-1

matrix of PEG 4000-PEG 6000 (1:1)

dimethyl silicone oil as condensate

dropping distance of 6.8 cm

proportion of matrix-volatile oil (3.7:1)

liquid temperature at 87.4 ℃ and upper temperature of condenser pipe at 7.9 ℃;average values of appearance grade

dissolve time limit and methyl-n-nonyl-ketone content were 82 points

16.4 min and 1.83 μg·g-1

whose deviation were 2.04%

1.49% and 1.61% by comparing with these predicted values

respectively. Conclusion: Central composite design and response surface methodology was suitable for optimizing preparation process of this preparation with good predictability

this study could provide a reference for development of Houttuyniae Herba preparations.