Modern power supplies must provide reliable, high-quality power. Therefore, it is important that a transmission line fault be identified accurately, reliably and corrected as soon as possible. A method for classifying fault type based on short time Fourier transform (STFT) is provided in this paper. STFT is a means of signal processing in which a Fourier transform (FT) is performed by setting a window function with a constant size. This transformation is used to analyze transients in the power system. In order to verify the suggested algorithm, the transmission system is modeled by EMTP-RV and line faults are simulated in the transmission line. This paper analyzes characteristics of STFT by using simulation results from MATLAB and classifies line faults by fault type. The simulation results show that the suggested algorithm is effective and valid for detecting fault types during line faults.