An Er-doped superfluorescent fiber source is designed and constructed with the double-pass forward configuration, which aims at high stability of its mean wavelength against temperature variation. As a result, thermal stability of mean wavelength better than 1 ppm is obtained against the temperature variation of ${pm}5^{circ}C$ around the optimum operating temperature. The optimum operating temperature can be tuned with the Er-doped fiber length and the pump power.