248 nm KrF excimer lasers have important applications in many areas such as photoetching and scientific research. The excimer laser for writing Fiber Bragg Grating was developed. The mechanical structure was designed and improved, and the key technologies including uniform discharge and preionization were analyzed. The laser performance was optimized by studying the impact of the charging voltage, the gas mixture and the total gas pressure on output energy and efficiency. The beam profile homogeneity, beam divergence angle and energy stability were measured and calculated. The repetition rate of the excimer laser is 1-50 Hz, and the maximal output efficiency is about 2.0%, and the maximal single pulse output energy is up to 360 mJ. The instability of output energy is less than 1.8% with charge voltage above 24 kV. Writing Bragg Grating in optical fiber core with a static phase-mask by the above laser as light source, of which results were analyzed and discussed.