The invention provides a fabrication method of a thin film transistor (TFT) substrate. The fabrication method comprises the following steps of forming a buffer layer, a data line and a source on the substrate by a first mask process, and arranging a first scanning line, a second scanning line and a gate on the buffer layer; forming a first insulation layer on the buffer layer and the gate by a second mask process, forming a second insulation layer on the data line, forming a first semiconductor layer on the first scanning line and the second scanning line, and forming a second semiconductor layer on the source; forming a first photoresist layer on the second insulation layer and the second semiconductor layer by a third mask process, forming a second photoresist layer on the first insulation layer, performing conduction on the first semiconductor layer to form a first conductor layer, forming a second conductor layer on the substrate, forming an electrical connection part on the first conductor part and the second insulation layer, and forming a drain on the second semiconductor layer. The scheme has the advantages the process is simple in step, the production efficiency can be improved, and the production cost is reduced.