Indium gallium zinc oxide thin film transistors (IGZO-TFT) were prepared by aqueous solution method, and the effects of different post-annealing temperatures (270, 300, 330, 360 and 400℃) on the electrical properties of IGZO-TFT devices with and without UV-assisted annealing conditions were investigated. It is found that the IGZO-TFT exhibites the best device electrical properties at the post-annealing temperature of 360℃, thus demonstrating that the aqueous solution method can prepare IGZO-TFTs at low temperatures of less than 400℃. Meanwhile, it is shown that at a post-annealing temperature of 360℃, compared with the non-UV-assisted annealed IGZO-TFT, the saturation mobility of the UV-assisted annealed IGZO-TFT increases from 1.19 to 1.62cm2/Vs, and the positive gate bias offset decreases from 8.7 to 4.6V and the negative gate bias offset decreases from -9.7 to -4.4V, thus demonstrating that UV-assisted annealing has activating and passivating effects on IGZO films, which can optimize the electrical properties of IGZO-TFT devices.