The condition for equilibrium oscillation of dual-wavelength erbium-doped fiber ring laser is derived from the average inversion level model. According to this condition, a novel experiment setup is built to measure the influence of pump power, mode losses and wavelength interval on the output power. Experiment results show that the multi-wavelength oscillation in erbium-doped fiber ring laser can be achieved by adjusting the loss spectrum of laser cavity, and the condition for equilibrium oscillation is valid when pump power is far away from the threshold point. The stability of variable optical attenuator has so great influence on the balance of dual-wavelength whose acceptable loss bias is less than 0.4 dB. However the stability of central wavelength of fiber Bragg grating (FBG) has little influence on the balance of dual-wavelength which won’t be broken by the wavelength bias less than 1 nm. Inhomogeneous effect of erbium-doped fiber allows tiny perturbation of the loss in state of equilibrium, which is helpful to improve the stability of the laser output power, and the power fluctuation of 1546 nm and 1556 nm over 30 minutes is less than 0.5 dB.