To study the mechanism of aqueous enzymatic extraction of oil from rapeseed, the enzymatic hydrolysis of rapeseed protein containing oil by alcalase was carried out at pH8.0 and 50℃. The results indicated that the particle size of the solid in milk influenced reaction velocity obviously, and the velocity increased greatly with the size decreasing. The overall rate of hydrolysis diminished exponentially versus the degree of hydrolysis. Based on this approach and experimental data, a kinetic model equation simulating the enzymatic hydrolysis of rapeseed protein containing oil with Alcalase was obtained and it could be used to guide and optimize the technology of aqueous enzymatic extraction of oil from rapeseed.