In order to solve the problem of wavelength control during the fiber Bragg grating fabrication, and to improve the precision of the existing solutions, a method based on the phase mask, including two steps of tension adjustment in the Bragg grating inscription and uniform ultraviolet irradiation, is proposed. The tension is adjusted by hanging weight at both ends of the fiber to make the grating central wavelength slightly smaller than the desired wavelength, then ultraviolet light is irradiated on the grating uniformly along the fiber to compensate the difference between the grating central wavelength and the desired wavelength. The error of grating wavelength is controlled within ±5 pm, and the change of the grating platform is small, which will not destroy the platform stability. Experiment result shows that the reflectivity of 1 cm long apodised Bragg grating reaches more than 30 dB. This method is simpler, more accurate and reliable compared with the existing methods.