An external cavity tunable semiconductor laser is designed, which is based on a traditional Littman-Metcalf structure. The semiconductor laser with a wide gain spectrum is served as the seed source of the internal cavity. Meanwhile, the external cavity feedback unit is composed of a blazed grating and a tuned mirror. The experimental results of no mode-hopping, high precision such as ±1.38 pm, high side-mode suppression ratio such as 84.34 dB and high stability such as power ±0.008 83 dB/1h, wavelength ±0.25 pm/1h, with tunable wavelength range of 1 479.96~1 599.96 nm are realized. The effective cavity length of the designed external cavity tunable semiconductor laser is about 50 mm, the maximum output power is 15.19 dBm, and the minimum output spectral linewidth is 18.89 kHz. The research is conductive to promoting the research of new ultra-high resolution spectral analysis systems and providing autonomous and controllable laser signal generation source.