The water content of crude oil is an important parameter in oilfield development. It plays an important role in determining the water production of oil wells and the location of the oil layer, in estimating crude oil production, and in evaluating the value of production. The problem of inaccurate measurement of the high and low water cuts has always existed in oilfield development. In this paper, a systematic method of applying quartz crystal microbalance (QCM) liquid phase detection technology to the water content measurement of crude oil is proposed, and the water content of six standard glycerol solutions is measured. The results show that the error between the theoretical and experimental values is very small (<3%) and that the magnitude of the error hardly increases at low and high water contents (increase <1%). Repeated experiments also verify the effectiveness of the method. Finally, the field measurement results of water content of crude oil confirm the applicability of the model. This method will help improve the measurement accuracy of the water content of crude oil over a wider range of water content, which is of great significance for the application of the QCM in oilfield development.