The invention discloses a pile supporting device and a steel sheet pile supporting method. The pile supporting device comprises a telescopic sleeve, a rear sleeve, a hydraulic cylinder, a threaded sleeve, a nut and snap ring flanges, wherein the outer side of the rear sleeve is provided with a plurality of snap ring grooves, and the two semicircular snap ring flanges are oppositely buckled in one of the snap ring grooves; the telescopic sleeve and the rear sleeve are connected in a sleeving mode through the snap ring flanges, and the threaded sleeve is sleeved with the other end of the rear sleeve; the nut is screwed on an external thread of the threaded sleeve, and the hydraulic cylinder is arranged inside the threaded sleeve; and a hydraulic cylinder support is fixedly connected with the other end of the threaded sleeve, and the other end of the hydraulic cylinder is connected with the rear sleeve. Compared with the prior art, the pile supporting device has the beneficial effects that the telescopic sleeve serves as a supporting part, pushing force of a power device is used for pushing a steel sheet pile, the length can be flexibly adjusted, and the application range is wide; and the pile supporting device is convenient and reliable to operate, small in size, simple in structure, convenient to construct and transport, large in supporting force, high in speed and high in work efficiency.