The rate equations of ytterbium-doped double-clad fiber lasers were solved by numerical simulation under principles of fiber interference loop and stimulated Brillouin scattering. The relationships between pulse repetition rate, pump power and couple ratio of the coupler which constructed the fiber interference loop were obtained. The relationships between average output power, pulse energy, pump power and couple ratio were also obtained by exploiting the model based on photon balance. A self-Q-switched Yb³⁺-doped double-clad fiber laser was employed experimentally to test how the pump power affect average power, pulse energe and pulse repetition rate respectively. The results show that both average power and pulse repetition rate can be increased by increasing pump power, and the increase of pulse energy needs to choose appropriate couple ratio other than the increase of pump power. It also shows that the second-order Stokes pulse will be stimulated if the pump power is high enough.