An oxide semiconductor thin film transistor, a manufacturing method and a display device thereof are disclosed. An oxide semiconductor thin film transistor comprises a gate insulating layer (22), an oxide semiconductor layer (24) and a blocking layer (25), wherein a first transition layer (23) is formed between the gate insulating layer (22) and the oxide semiconductor layer (24), the oxygen content of the first transition layer (23) is higher than the oxygen content of the oxide semiconductor layer (24). The oxide semiconductor thin film transistor enhances the interface characteristic and the lattice matching between the oxide semiconductor layer (24) and the blocking layer (25) to improve the stability of the thin film transistor better.