The diffraction characteristics of the linearly chirped phase mask is investigated using rigorous coupled-wave theory. The results show that the groove depth and duty cycle of phase mask must be controlled within the range of 242～270 nm and 0.37～0.50 respectively, in order to make the zero order diffraction efficiency less than 2% and the ±1 order diffraction efficiency more than 35%. Based on the above analysis, a linearly chirped phase mask with the center period of 1000 nm, ruled area of 100 mm×10 mm and chirp rate of 1 nm/mm has been fabricated by a new technique, which combines holographic-ion beam etching and reactive ion beam etching. The experiment and simulation both indicate that the Ar ion beam etching can modify the initial photoresist grating profile and produce a suitable duty cycle under the CHF3 reactive ion beam etching. Experimental measurements show that the zero order diffraction efficiency is less than 2%, with the ±1 order diffraction efficiency more than 35% and the maximum nonlinear coefficient of 1.6%. Theoretical analysis also indicates that the phase masks can be used to fabricate the UV written chirped fiber Bragg gratings.