Abstract: The fast matrix solving is the key of the moment method when computing the electrically large issues. LU decomposition is a efficient algorithm for solving linear equations. In this paper, Doolittle LU Decomposition is described detailedly. Based on the decomposition characteristics, a parallel solving method looping over squares is proposed in MPI (Message-Passing interface) parallel environment. The experiments indicate that the method can decrease communication quantity between processes and accelerate computing speed efficiently.