The invention discloses a multifunctional supercritical water thermal combustion device. The multifunctional supercritical water thermal combustion device comprises three parts, namely, an upper end cover, a straight cylinder body and a bottom end socket, wherein the upper end cover is arranged at the upper end of the straight cylinder body, a radial coaxial combustor pipe is arranged on the upper end cover and comprises a core pipe and a mixing pipe of a fuel solution inlet, an oxygen inlet passage is formed by a circular gap between the core pipe and the mixing pipe, and a waste liquid inlet passage is formed by a circular gap between the mixing pipe and a spray nozzle pipe at the bottom part of the upper end cover; the straight cylinder body is divided into an outer cylinder and an inner cylinder, the outer cylinder is a pressure bearing wall, a combustion reaction chamber is formed by the inner cylinder, a cooling water passage is formed by a circular cavity gap between the walls of the inner cylinder and the outer cylinder, and the inner cylinder can be changed into a water-cooling wall or a porous evaporation wall; an inlet of reacted fluid is arranged on the bottom end socket. According to the multifunctional supercritical water thermal combustion device disclosed by the invention, the changeable inner cylinder enables a reactor to carry out a research on supercritical water thermal combustion characteristics of an evaporation wall type reactor as well as a research on supercritical water thermal combustion characteristics of a cooling wall type reactor.