Abstract: In this paper, the formulae of the vibration response and power flow in beam-stiffened plates in the far field with force excitation applied on the plate, have been obtained by using the Steepest Descent integral method, and the power flow characteristics have also been studied through computer simulation, it is shown that the stiffener acts as an extra lineal excitation applied on the plate and will change the power flow characteristics of the infinite plate; the greater the stiffness and the less the distance between exciting point and stiffener, the greater the influence. At last, experiments have been carried out by using the dual-accelerometer cross spectrum measurment technique, the test data agree well with the theoretical results.