The utility model relates to a liquid-level measuring device for an oil-gas separator, which is applied to an oilfield oil-gas separator. A glass-pipe liquid-level meter is installed on a separator tank body, and the upper end of the liquid-level meter is communicated with the separator tank body. The lower end of the liquid-level meter is connected with a guide pipe, the guide pipe penetrates through the separator tank body, the end part of the guide pipe in the separator tank body is provided with a union (joint) and connected with a vertically-downward brine pipe through the union, and the brine pipe is communicated with a brine bag. The brine bag is fixed at the bottom of the separator, a pipeline is connected between the brine bag and a brine filler, and an electromagnetic valve is connected to the pipeline between the brine bag and the brine filler. The brine is filled in the brine bag and the liquid-level meter through the brine filler. The utility model has the effects that: the freezing and blocking phenomena generated by the crude oil in the liquid-level meter are solved, and the real liquid level in the oil-gas separator can be reflected by the liquid-level meter, so that the accuracy of the liquid-level meter of the separator is greatly improved.