Preparation method of thin film transistor, thin film transistor and display panel

The invention relates to a preparation method of a thin film transistor, the thin film transistor and a display panel. The preparation method comprises the steps of: sequentially preparing a first metal layer and a second metal layer on the surface of one side, far away from a gate insulating layer, of an active layer, then patterning the first metal layer and the second metal layer, and preparing a third metal layer on the surface of one side, far away from the first metal layer, of the patterned second metal layer by adopting an electroplating process, wherein the third metal layer further covers the side wall of the second metal layer and the side wall of the first metal layer. The third metal layer is prepared by adopting the electroplating process, and the third metal layer can grow according to the pattern of the second metal layer, so that patterning processing on the third metal layer is avoided, and the etching abnormal phenomenon of the source and drain electrode layer in the prior art is further av