With the waveguide corner mirror structure and the effective combination of the Goos-Hanchen （GH） spatial shift and the thermo-optical effect refractive index modulation， a digital thermo-optical switch structure of waveguide reflected mode is proposed. The GH spatial shift is optimized under the condition of a given incident angle， and the reflected beam has a larger jump under an eigenstate with the GH effect. On a silicon-on-insulator platform with a 1.0 μm thick silicon film， the guided mode eigenstate matching between the single-mode input waveguide and the multimode interference waveguide structure verifies the function of a 1×3 digital optical switch. In experiment， the optical loss caused by the device structure is 0.3 dB， the switching power is 130~150 mW， the switching time is about 50 μs， and the isolation between adjacent output ports is 15 dB. The comparison with the latest results of the Mach-Zehnder interferometer 2×2 thermo-optic switch and the newly emerging plasma effect thermo-optic switch shows the advancement of this digital TO switch.