The invention discloses a depth measuring device which comprises a case. The top or the side of the case is provided with a handle, and a motor and a turntable driven by the motor are arranged in thecase. The turntable is wound with a measure tape, one end of the measure tape is fixed onto a rotating shaft of the turntable, and the other end of the measure tape penetrates a through slot at the bottom of the case and then hangs a weight. A circuit board for driving the motor to rotate forwards or reversely is further mounted in the case, and a switch of the circuit board is arranged outside the case or outside the handle. Therefore, the depth measuring device can avoid complex manual operation due to the fact that a measure tape is paid off or taken up by rotating the turntable with handsin the prior art; mechanical automated depth measurement can improve working efficiency; meanwhile, compared with the mode of measuring the depth of a liquid tank by hand-cranking the measure tape, measuring precision can be improved.