Abstract: Aiming at the difficulties of testing parametric faults,an approach based on wavelet filter bank is presented. Subband filtering to test response signal is achieved by virtue of wavelet filter bank. The computation of correlation coefficient,correlation function,covariance function,coherence function and power spectrum is followed on the subband filtered.The signature extraction to analog response signal is carried out based on the above five operations.As a result,the difficulty to distinguish fault-free and faulty circuit by a single signature can be solved effectively.Signature with clearly apparent difference between normal and faulty circuit is chosen to diagnose faults.Experimental results show that our approach based on pyramid type Haar wavelet filter bank is of high effectiveness in testing parametric variation of analog component.