Commercially available blue-violet edge-emitting semiconductor laser diode with a wavelength of 405.5 nm is characterized and then operated in an external cavity with a Littrow configuration in our laboratory. A resonant cavity is formed between the blazed grating and the rear facet of the laser diode, which improves the performance of the laser diode greatly. The results show that the threshold current of the semiconductor laser diode decreases by 27%, indicating high coupling efficiency between the external cavity and inner cavity. Besides, by changing the angle of the blazed grating, the total wavelength tuning range can reach up to 7 nm.