To identify the type of noise in an Interferometric Syntheic Aperture Radar (InSAR) interferogram and facilitate more effective data processing, especially for interferogram filtering based on wavelet transform, we developed a novel method for identifying the noise type and estimating the noise level. This method combines wavelet transform with logarithmic transformation and includes an in-depth analysis of the characteristics of interferogram wavelet coefficients from the viewpoints of energy distribution and statistical interpretation. First, we investigated the energy distribution characteristics of low-frequency subband wavelet coefficients before and after the logarithmic transformation to identify the noise type of the interferogram. On this basis, the noise level could be estimated using high-frequency subband wavelet coefficients. From the analysis results of this study, we conclude that the noise type of the InSAR interferogram is additive noise, the high-frequency coefficients show a Gaussian distribution, and the noise level can be estimated by a high-frequency subband on one scale. These results provide further scope for noise analysis and processing of InSAR interferograms based on wavelet transform.