Abstract: The adaptive Chirplet decomposition contains a lot of unknown parameters and the decomposition methods are time-consuming. Motivated by this， a method for adaptive Chirplet signal decomposition based on envelope fitting is proposed. The chirp rate is estimated by integrating the quadratic phase function as time. The time center of the energy concentration and the spread of the pulse is estimated by curve fitting of the signal envelope. The estimating precision of estimated chirp rate and original frequency is improved by using the phase value around the main lobe of envelope to revise them. The procedures for single-component and multi-components Chirplet decomposition are presented. Also， the CRB of parameter estimation for Chirplet under normal gauss circumstance is deduced. Simulation and experimental results demonstrate the validity of the proposed method.