Usually, conventional incoherent weather radar is used to provide only the information on the position of a weather target and its radar reflectivity by detecting echo intensity. In this paper the fluctuating spectrum and its spectral width are estimated by fast Fourier transformation of the discrete sample of precipitation echoes at a specified position with a microcomputer(Apple Ⅱ) connected with a home-made incoherent weather radar 713. Based on the relation between fluctuating spectrum and Doppler spectrum, calculation has been performed for the width and shape typical of the Doppler velocity spectrum, which are very useful in meteorology.