The most basic problem in numerical analysis (methods) is the root finding problem. In this paper we are interesting in new numerical method which based on the Modified Bisection Method(MBM) referred to by Tanakan superficially and he didn't know her as a numerical method for finding the roots of a function. Hence in this study we define a new numerical method base on MBM with error bound and the number iterations necessary. Finally we present our new MBM for multi-roots with the R software.