In this paper Haar wavelet integral operational matrices are introduced and the n applied to analyse linear time-varying systems. The method converts the origi nal problem to solving linear algebraic equations. Hence, computational difficulties are considerably reduced. Based on the property of time-frequency localization of Haar wavelet bases, the solution of a system includes both the frequency information and the time information. Other orthogonal functions do not have this property. An example is given, and the results are shown to be ver y accurate.