The invention relates to a self-adjustable variable buoyancy underwater platform and belongs to the field of ocean monitoring. The platform comprises an emission device, an underwater monitor, a stable plate, a control unit, a battery pack, a pressure-resisting shell, an oil storage tank, a depth sensor, a depth adjusting mechanism, a hydraulic pulse control valve, a bidirectional quantitative hydraulic pump and a motor, wherein the depth adjusting mechanism comprises a connector body, an oil bag end cover, an oil bag and an oil bag protective cover; the platform adopts the motor to drive the bidirectional quantitative hydraulic pump to realize oil injection or oil pumping of the depth adjusting mechanism so as to achieve the self-adjusting function of ascending or descending on the platform; and a hydraulic loop system is internally designed with the hydraulic pulse control valve so that the self-locking performance of a driving motor can be ensured, the inversion in a large-depth ocean environment can be prevented and the whole power consumption of the platform can be reduced.