The utility model discloses a subsection closing device for a hydroelectric generating set, which comprises an electromagnetic sliding valve (1), a subsection valve body (5) provided with a subsection inner cavity, a top cover (6), a bottom cover (2) and a one-way valve (3), wherein the electromagnetic sliding valve (1) is provided with an oil supply port (P), a first control oil port (A), a second control oil port (B) and an oil return port (T); the top cover (6) and the bottom cover (2) are connected with the subsection valve body (5) in a sealing manner; an up-down sliding subsection valve core (4) is arranged in the subsection inner cavity (4); an upper end part valve disk (I) and a lower end part valve disk (L) are arranged at two ends of the subsection valve core (4); an intermediate valve disk (G) is arranged between the upper end part valve disk (I) and the lower end part valve disk (L); and a throttle port (J) is arranged on the intermediate valve disk (G). The subsection closing device has the advantages of high reliability, quick dynamic response and high structure integration; the cost is reduced; the one-way valve is connected with a subsection body in a plate type, so that the occupied space of the installation can be reduced; and by adopting a fine tuning throttle port technology, the subsection closing device is convenient to debug and has high control precision.