By using the determination on the change of EGCG concentration with time in the course of extraction by water or ethanol, and the application of mathematical model derivation and equation regression methods, the kinetic rule in extraction of tea EGCG was investigated and disclosed in this paper. An optimized extracting time and kinetic equation in different conditions were put forward. Results showed that the equation optimization was succeeded and the extraction of EGCG complied to diffusion kinetic rules.