A wavelength tuning method suitable to watt-level continuous-wave single frequency solid-state laser (CWSFL) at 1.5 µm was proposed. Based on a dual-gain-medium resonator design, the laser wavelength can be tuned by manipulating the combined net gain spectrum. Comparing with the traditional tuning method, the wavelength tuning range was eight times broader and extended to 0.438 nm, the maximum laser power was raised up to 0.64 W, which was the highest record for the 1.5 µm CWSFL to the best of our knowledge. The laser intensity noise reached the shot noise limit at the analysis frequency above 3.5 MHz. Wider wavelength tuning band of 5.58 nm can be expected when the same resonator design including two gain media with different doped concentrations was used, according to our theory.