In this paper, indium gallium zinc oxide thin film transistors (IGZO-TFT) were prepared by aqueous solution method, and the effects of different post-annealing temperatures (270 °C, 300 °C, 330 °C, 360 °C and 400 °C) on the electrical properties of IGZO-TFT devices with and without UV-assisted annealing conditions were investigated. It was found that the IGZO-TFT exhibited the best device electrical properties at the post-annealing temperature of 360 °C, thus demonstrating that the aqueous solution method can prepare IGZO-TFTs at low temperatures of <400 °C. Meanwhile, it is shown that at a post-annealing temperature of 360 °C, the saturation mobility of the UV-assisted annealed IGZO-TFT increases from 1.19 to 1.62 cm²V^-1s^-1, and the positive gate bias offset decreases from 8.7 to 4.6 V and the negative gate bias offset decreases from -9.7 to -4.4 V, compared with the non-UV-assisted annealed IGZO-TFT, thus demonstrating that UV-assisted annealing has activating and passivating effects on IGZO films, which can optimize the electrical properties of IGZO-TFT devices.