Abstract: The accurate estimation of ultrasonic Time-of-flight (TOF) is essential in ultrasonic object loaction system. In this study, a new method for TOF estimation through envelope is proposed. Firstly, the Hilbert Transform (HT) is used in ultrasonic signal processing in order to extract the envelope of the echo and to reduce the computational burden. Then, the wavelet denoising technique is applied to the extracted noisy envelope to improve the estimation accuracy. Finally, the echo parameters are estimated by using a Modified Gauss Newton (MGN) based nonlinear Least Squares (LS) estimation method. Numerical simulation has been carried out to show the performances of the proposed method in estimating TOF of ultrasonic signal.