Let p be an odd prime. In this paper we write down the functional equations of Siegel Eisenstein series of degree n, level p with quadratic or trivial characters. First we study the U (p) action in the space of Siegel Eisenstein series to get U (p)-eigen functions. Secondly we show that the functional equations for U (p)-eigen Eisenstein series are quite simple and easy to write down. Consequently the matrix that represents functional equations of Siegel Eisenstein series are given by the products of simple matrices.