The invention provides a buoyancy regulating apparatus, which comprises a shell, a buoyancy converting device, an oil way control device, a power device and a pressure monitoring device, wherein the buoyancy converting device comprises a two-way oil cylinder and an oil sac which are mounted on the shell respectively and are further communicated with each other; the area of one end of a piston of the two-way oil cylinder is less than that of the other end; further, the end with the small area is in contact with seawater; the oil way control device controls the connection and the disconnection of an oil way between the two-way oil cylinder and the oil sac; the power device enables oil between the two-way oil cylinder and the oil sac to flow through the oil way control device; the pressure monitoring device is used for monitoring the changes of the pressure and the displacement of the buoyancy converting device and triggering the power device to work. According to the piston of the two-way oil cylinder of the buoyancy regulating apparatus, the internal pressure of an apparatus can be compensated from the pressure of the seawater by utilizing an area difference between two ends; a pressure difference between two ends of a two-way oil pump is greatly reduced; a high-pressure oil pump does not need to be selected and used; requirements on an oil pump and an internal component are greatly decreased; the cost is decreased; moreover, the cruising ability is improved in the condition that the power consumption is decreased.