In the process of power quality signal acquisition and transmission, noise interference will be introduced due to the influence of the external environment. It is an important prerequisite for power quality control to effectively denoise and retain the mutation information. An adjustable threshold function is given in this paper. By controlling the adjustable parameter, the new threshold function can be changed between soft and hard threshold functions. The wavelet coefficient energy factor is introduced, and the scale with the largest energy is taken as the characteristic scale. On this scale, the sub interval energy higher than the scale energy is the effective interval. Then a new threshold method using effective interval local threshold is proposed. In addition, considering the propagation characteristics of the wavelet coefficients of noise and signal with different scales, an operator is introduced to modify the threshold. Compared with the traditional global threshold method, the local threshold method based on the effective interval can better reflect the characteristics of wavelet coefficients. The simulation experiments prove that the proposed method not only improves the denoising performance, but also retains the disturbance mutation information. After denoising, the disturbance location is accurate, and the position of the modulus maxima can well reflect the occurrence and end time of the disturbance.