Abstract: OBJECTIVE To discover the in vitro release mechanism of bergenin β-cyclodextrin (β-CD) inclusion complex osmotic pump tablets. METHODS Three rate-limiting factors influencing drug release from dosage form(the semi-permeable membrane, tablet core and delivery orifice) were investigated to study the main pharmacodynamics of its driving and the zero order release mechanism. RESULTS The influx of water that passed the osmotic pump tablet was greatly less than the drug dissolution rate from tablet core and the bergenin release rate. Corrosion mechanism and diffusion mechanism have effect on drug release from osmotic pump tablets. CONCLUSION A variety of mechanisms have effect on drug release of the bergenin β-CD inclusion compound osmotic pump tablets, the main driving force of release is the membrane osmotic pressure difference inside and outside, the water influx through the membrane is the rate-limiting step, accordingly, the drug release had obvious characteristic of zero order release.