NOVELTY - The apparatus comprises a center tube passes through a center of a main mixer, a lithium solution tube installed in the central tube and into which lithium solution is injected, an iron/phosphorus solution tube installed in the central tube and into which iron/phosphorus solution is injected, multiple supercritical water tubes installed in the main mixer and penetrated through a center of the central tube for containing mixed solution of lithium solution and iron/phosphorus solution, and a shut-off valve installed at a front end of the main mixer to prevent clogging in the main mixer.    USE - The apparatus is useful for performing continuous hydrothermal synthesis process in super critical condition (claimed) during the manufacture of a lithium-ion secondary battery of a hybrid electric vehicle (HEV) and a mobile device.    ADVANTAGE - The apparatus is capable of performing stable continuous hydrothermal synthesis process to improve supercritical water productivity, facilitates removal of scale, and minimizes particle dispersion due to flux variation.    DETAILED DESCRIPTION - The apparatus comprises a center tube passes through a center of a main mixer, a lithium solution tube installed in the central tube and into which lithium solution is injected, an iron/phosphorus solution tube installed in the central tube and into which iron/phosphorus solution is injected, multiple supercritical water tubes installed in the main mixer and penetrated through a center of the central tube for containing mixed solution of lithium solution and iron/phosphorus solution, and a shut-off valve installed at a front end of the main mixer to prevent clogging in the main mixer. A symmetric connection unit is installed on both sides of the lithium solution tube, the supercritical water tube and the central tube. The water tubes are inclinedly connected to extension direction of the center tube. The water tubes, the lithium solution tube and the central tube are connected with each other to form an acute angle. A filter filters the powder of a cathode active material generated in a reactor. A heat exchanger maintains the state of the mixed solution in the main mixer at high temperature. A heater passes through the heat exchanger to heat the water. An INDEPENDENT CLAIM is included for a method for performing continuous hydrothermal synthesis process in super critical condition.