Dr. Hanaoka's theory and Prof. Nishiyama's theory are well known as a linearized theory of cavity flow past a hydrofoil in which a source-sink method is applied. Comparing with experimental data of thick hydrofoils, the calculated thickness of cavities is about two times of experiment, although close agreement is obtained within comparative calculations. Authors have attempted to calculate the characteristics of partially cavitated thick hydrofoils by solving the non-linear equation expressing the velocity on a thick hydrofoil in which a shape of cavity is included as an unknown parameter. Herewith, the method for solving the non-linear equation is presented, and numerical calculation results are compared with experimental data for a shape of cavity and pressure distribution on a partially cavitated hydrofoil.