The Mesozoic volcanic suite located in the Tianmushan Mount., northwestern Zhejiang Province, China, is, in ascending order, composed of rhyolite, dacite and andesite. A model of physically and chemically zoned magmatic chamber has been used for explaining this reversed compositional sequence. Gradients of temperature, density and viscosity in the chamber have been established according to some thermodynamic methods. Modeling for major and trace elements supports the idea that fractional crystallization is a main mechanism responsible for the chemical variation. The settling velocities of observed minerals in different magmas, which are estimated from Stocks' law, indicate that gravitative settle is impossible, especially in the acid magma. Thus, convective fractionation (Huppert et al., 1988) is considered most probably to be the process accounting for the fractional crystallization in the zoned chamber.