A new method that could be used to quantify the water content in oil for marine-borne machine was discussed in this paper. For water has three different status existing in oil, it is hard to test the total content of water in oil. And many currently used methods are not convenient for on-site testing or not able to distinguish water from the metal particles. But the water molecular has distinct absorption bands in infrared section at 3500∼3150cm -1 . An experiment set was designed to accomplish the experiment and verify our assumption. Experiment shows that there is a linear relation between the total absorbed energy in 3500∼3150cm -1 and the percentage of water content in oil. The research work in this paper gives us an idea to design an instrument to measure and warn people who monitor the excess of the amount of water in different kind of oil in machine.