Ge20As20Se15Te45 chalcogenide glass was prepared by a melt-quenching method. Testing results show that this glass posses high nonlinear characteristics and wide infrared transmission windows in the infrared region. The third-order nonlinear coefficient was tested to be n2=6.72×10-18 m2/W @ 4 μm by a Z-scan technique. Two kinds of chalcogenide glass infrared fiber grating optical switches were designed with this glass. The reflection spectrum and grating wavelength shift of optical switches were calculated with the distributed time-domain transfer matrix method (TD-TMM) and non-linear coupling equations. Results show that the Bragg wavelength can be flexibly tuned by modulating the input intensity and optical switch can be achieved. It was found that the power threshold is about 1.6 GW/cm2 for an optical switch with a modulation depth of 1×10-3 in a uniform chalcogenide Bragg fiber grating and the power threshold can be significantly reduced to about 210 MW/cm2 in a phase-shift chalcogenide fiber grating with a modulation depth of only 3×10-4.