The oil well liquid level depth measuring device for oil production in oil field consists of a computer, a D/A converter, a power amplifier, a loudspeaker, a microphone, an adjustable amplifier, an A/D converter, a horn cover and a flexible steel hose. It features the computer includes a PN code generator, one local code generator, a phase comparator, a correlation judging unit, a phase regulatorand a carrier modem. The liquid level depth measurement includes the following steps: phase modulating the carrier with PN code, sending the sound wave through the transducer to the well target, receiving the reflected sound signal with the well head microphone and treating the reflected sound signal.