A method for quasi-synchronous tuning of wavelength or frequency of grating external-cavity semiconductor laser and a corresponding semiconductor laser are provided. A grating or mirror is rotated around a quasi-synchronous tuning point (Pq) as rotation center, so as to achieve the frequency selections by grating and resonance cavity in quasi-synchronous tuning, wherein the angle of the line between the quasi-synchronous tuning point (Pq) and a conventional synchronous tuning point (P0) with respect to the direction of light incident on the grating is determined according to the angle difference between the incidence angle and diffraction angle of light on the grating. According to present invention, approximately synchronous tuning of laser is achieved with a simple and flexible design.