Objective:To study on drug release mechanism of panax notoginsenosides microporous membrane osmotic pump tablets（PNSMPOP）.Method: With comparing drug release behavior of PNSMPOP in different osmotic pressure medium and investigating effects of different release methods on drug release velocity

to investigate release mechanism of this preparation.Result: Drug release velocity declined with difference of osmotic pressure between inside and outside of coating film increased;Drug release behavior was similar between in distilled water and pH 6.8 phosphate buffer

but release rate decreased in pH 1.0 hydrochloric acid solution;There was no significant influence on drug release by different drug release methods.Conclusion: This tablet released mainly in gradient-driven mechanism of osmotic pressure between inside and outside of membrane

a small amount of drug released by directly spread.