This paper investigates problems associated with relaxation oscillation and output powers in homogeneously broadened four-level lasers having nonuniform population inversion and photon densities along the laser axis. The rate equation for the population and photon number of four-level lasers has been solved with considering the diffusion of excited states. Numerical solution shows that the energy migration between lattice sites significantly increases the frequency and damping constant of the relaxation oscillations together with the obtainable power from the spatially hole-burned lasers.