Accurate acquisition of time of flight (TOF) is essential for high-precision ultrasonic thickness measurement. A time delay estimation method for ultrasonic thickness measurement signal based on fuzzy variable-step least mean square (LMS) was proposed, addressing the issues that the inherent contradiction between the convergence speed and the steady-state error of the fixed-step LMS algorithm in the traditional ultrasonic signal time delay estimation, and the poor adaptability of the existing variable-step algorithm under non-stationary echo signals due to the dependence on the fixed function model. The time-varying characteristics of ultrasonic echo signal were analyzed, and the single error feedback mechanism was abandoned. The local correlation coefficient error and its variation between the output signal and the desired signal were extracted as the dual input characteristics of the fuzzy controller. The zero-order Sugeno fuzzy inference system was designed, and the nonlinear mapping rule between the input feature and the step size factor was established to realize the adaptive dynamic adjustment of the step size factor. The simulated echo signals were used to carry out simulation tests under different signal-to-noise ratios. The results show that compared with the fixed step size LMS algorithm, the hyperbolic tangent function variable step size LMS algorithm and the fuzzy variable step size LMS algorithm based on instantaneous error, the comprehensive performance of the proposed method is better. The steady-state offset error is significantly reduced while ensuring rapid convergence, with higher measurement accuracy and anti-noise performance. The experimental platform of ultrasonic thickness measurement was built, and the thickness measurement experiments were performed on gauge blocks. The results show that the relative errors of the proposed method for different thickness gauge blocks are all smaller than that of the other three LMS algorithms, and the maximum relative error is 0.71 %. The fuzzy variable step size LMS time delay estimation method can provide feasible scheme selection and technical support for high-precision ultrasonic TOF calculation, which is conducive to promoting the development of ultrasonic nondestructive testing technology and has certain engineering application value.