Trace water has a significant impact on the electrical performances of the insulating oil, such as the dielectric loss factor, resistivity. So there is an important significance to investigate the influence of insulating oil by trace water, and monitor its operating status with effective measures. First, it is necessary to prepare the insulating oil samples with different water content and treat them 8 hours with ultrasonic oscillator, and observe microscopic images about the water-oil mixtures in order to study their relative uniformity and stable time, in the way it can be concluded that the relative uniformity can be kept favorable during the 25 min stable time for free water and emulsification water in oil; Based on this conclusion, the dielectric loss factor, resistivity were tested and the electrical performances of insulating oil with different water content in oil can obtained by analyzing these data; Then, the absorbance value of the different water content in oil at the spectral wave number of 1 640, 3 400, 3 450, 3 615 cm-1, with the mid-infrared spectral scanning and analyzing to the different water content in oil, Therefore, combined the water absorbance values by the mid-infrared spectral scanning and analyzing with the experimental data of dielectric loss factor value, resistivity value of oil samples. The results shows that the absorbance value of the different water content in oil has a significant difference at the spectral wave number of 1 640, 3 400, 3450, 3 615 cm-1, their correlation coefficient are 0.964 1, 0.984 8, 0.984 5, 0.944 0 between the absorbance value and water content at the spectral wave number of 1 640, 3 400, 3 450, 3 615 cm-1, it can be obtained that the absorbance value of sample of moisture in the corresponding characteristic wave number can better reflect the change trend of water content; there is the highly relative of water absorbance values at the spectral wave number of 3 400 and 3 450 cm-1 with the trends of oil dielectric loss factor values, their correlation coefficient are 0.860 6, 0.863 6; and relative of water absorbance values at the spectral wave number of 1 640 and 3 615 cm-1 with the trends of oil resistivity values, their correlation coefficient is -0.931 5 and -0.968 0, this result can be lay the foundation research for monitoring the trace water in oil.