Adopting modified Sagnac interference grating writing system, the fiber Bragg gratings were written in two kinds of As2S3 chalcogenide fibers with different cladding diameter by use of a near bandgap light at 532 nm and +1/-1 diffracted orders phase mask, and the gratings dynamic characteristics during the exposure were studied. It is found that the depth of grating transmission peak in low-loss As2S3 chalcogenide fiber increases with a decrease of the cladding diameter. During exposure, the Bragg wavelength shifts fast towards short wavelength at first, and then with increasing exposure time restores slowly towards long wavelength. At exposure time from 800 s to 1000 s, the good quality Bragg grating with about -2.6 dB bandgap and about 0.37 nm bandwidth in transmission spectra was fabricated in As2S3 chalcogenide fiber with about 140 μm cladding diameter. In addition, an analysis of photosensitivity in the As2S3 chalcogenide fiber core shows that the refractive index modulation amplitude and the change of average refractive index with the exposure time can achieve to be on the order of 10-4 and 10-3, respectively.