Abstarct: One of the most important problems in civil engineering is evaluating soil settlements over time. In the classical method(Terzaghi method) that has been the basis of consolidation settlement calculations for the past, the amount of consolidation of the soil is calculated by assuming a constant coefficient of consolidation over the time of consolidation and in the depth of the soil. In clayey soils due to low permeability, water outflow from the soil takes place after a long period. In this regard, the estimation of the settlement of consolidation is necessary. In some cases, the amount of final settlement has been observed for several years due to the construction of a structure up to 2 meters. If this value is not predicted, it will cause irreparable losses. Due to the specifications and the nonlinear behavior of soils, the value of consolidation coefficient in a soil laxyer is not constant, and it changes with time and depth; so the real value of consolidation settlement is different from the amount calculated by classical theory. in this research, using the haar wavelet mathematical method, the equation of consolidation is solved in both linear(classical) and non-linear methods. The wavelet method is one of the new methods of solving differential equations that are less used in geotechnical engineering. One of the aims of the present study is to develop this method and to use it in geotechnical issues and to solve them efficiently. Due to the wavelet-solving process compared to other methods of solving differential equations, the computational speed is faster and the solving process is easier. Due to the difference between the results obtained from the classical method and the actual amount of consolidation ، in this study ، the soil consolidation equation is solved by considering the variability of the coefficient of consolidation with time and depth by the Haar wavelet method and its results are compared with the classical solution of the consolidation equation. The results show that the excess pore water pressure in the soil calculated from the classical method with a constant coefficient of consolidation is less than the one calculated from the nonlinear approach, indicating that the classical method estimates the consolidation duration less-than reality. In the end, the results of the wavelet method compare with the result of the finite difference method and the strengths and weaknesses of the wavelet method are compared to other methods of solving differential equations.