This paper aims to find an approximate solution for the nonlinear differential equation of first order Cauchy problem. To solve this problem we are going to study one variant of linearization method, in which the nonlinear terms are discarded or are linearzed with the help of special construction to find solution at the initial moment of time, or at any bounded point. This method is proved by the help of the estimation of closeness of the exact and linearized solutions by (uniform, integral and step by step procedures). This estimation has important value in this work.