Thin film transistor, manufacturing method thereof, display substrate and display device

The invention provides a thin film transistor, a manufacturing method thereof, a display substrate and a display device, and belongs to the technical field of display. The thin film transistor, the manufacturing method thereof, the display substrate and the display device can solve the problems that an existing thin film transistor, an existing display substrate and an existing display device are complex in manufacturing process, long in manufacturing cycle, low in yield and high in production cost. According to the thin film transistor, the manufacturing method thereof, the display substrate and the display device, a protection layer and an oxide active layer form an oxide active layer graph through a one-time graph composition process, one time of graph composition process is omitted compared with the prior art, and the thin film transistor is made to be easy in manufacturing process, short in cycle, high in yield and low in production cost; annealing is carried out in oxygen bearing atmosphere, and thus damage to the oxide active layer by plasma when a source electrode and a drain electrode are formed can be repaired; meanwhile, the contact side of the oxide active layer and the contact side of the protection layer are respectively provided with a transition area, and the off-state current of the thin film transistor can be lowered.