In recent years, with the booming of high-tech industry, there are many high-precision power electronic equipment being used. Most of them can not afford the transient changes in electricity. Therefore, this paper presents adaptive linear filtering (ADALINE) method for detection of voltage fluctuation. General methods for detecting the voltage variation is to calculate its root-mean-square value, which needs to calculate an integer multiple of the signal period in order to display the complete the effective energy of signal. If the calculation is not performed with the integer multiple of the signal cycle, the estimation results would be inaccurate. In this paper, ADALINE method is applied to detect the variation of voltage in the power system. ADALINE can accurately detect changes in the condition of the voltage value and then displayed on the amplitude- time graph. Finally, Lab VIEW program is used to give a simple test.