A thin film transistor includes a gate electrode, an active layer, a gate insulating layer located between the gate electrode and the active layer, and a source electrode and a drain electrode electrically connected to the active layer. The active layer includes a channel layer and at least one channel protection layer; a material of each of the channel layer and the at least one channel protection layer is a metal oxide semiconductor material. The at least one channel protection layer is a crystallizing layer, and metal elements of the at least one channel protection layer include non-rare earth metal elements including In, Ga, Zn and Sn.