The invention discloses a low-power-consumption wideband single-compartment-ball sea seismograph which comprises a plastic shell, a glass instrument compartment ball, a variable-buoyancy mechanism and a weight upspring frame. The glass instrument compartment ball is fixedly mounted in the plastic shell, the variable-buoyancy mechanism is positioned at the top end of the plastic shell, and the weight upspring frame is positioned at the bottom end of the plastic shell; the variable-buoyancy mechanism and the weight upspring frame are fixedly connected by a tensioning steel wire to fix the plastic shell in the weight upspring frame. The sea seismograph integrates an independently developed wideband seismograph (30s-100Hz) with a water sound pressure sensor mounted outside an instrument, thereby being capable of realizing multipurpose seaquake detection.