A method of preparing IGZO thin film transistor is provided. The method includes. step S1, using a first mask on a first metal layer to form a grid electrode, and sequentially forming grid insulating layer, IGZO semiconducting layer and second metal layer on grid electrode; step S2, coating photoresist layer on second metal layer, and exposure developing photoresist layer by second mask, and simultaneously etching second metal layer and IGZO semiconducting layer by hydrogen peroxide, and second metal layer is formed to source electrode and drain electrode by etching; step S3, forming passivation layer on source electrode and drain electrode, and forming a via hole above drain electrode by third mask; step S4, forming pixel electrode on passivation layer by fourth mask, and pixel electrode is connecting to drain electrode by via hole.