An all-optical switching model system comprising a single pulsed pump beam at 355 nm and a cw He-Ne signal beam at 632.8 nm was demonstrated with 2-(2'-hydroxyphenyl) benzothiazole(HBT) in five different polar solvents. The origin of the optical switching effect was discussed, and it was verified that fast excited state intramolecular proton transfer (ESIPT) of HBT and the slow thermal effect of solvent together induced the change of the refractive index of HBT solutions, which lead to the signal beam deflection and dominated the optical switching "off" and "on" states, respectively. The slow thermal effect of solvent results in the "tail" phenomenon of the optical switching recovery, and reducing the signal beam waist radius is a viable means for accelerating the recovery of the optical switching. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitivity optical switching devices. This work provides a theoretical as well as experimental basis for the production of ultra-fast all-optical switching device.