Thin film transistor and preparation method therefor, array substrate and display

A thin film transistor and a preparation method therefor, an array substrate and a display. The thin film transistor comprises: a gate (200), a gate insulating layer (201), an active layer (300), a source (401) and a drain (402). The active layer (300) comprises a first active layer (301) and a second active layer (302), the first active layer (301) is arranged at one side close to the gate insulating layer (201), and the second active layer (302) is arranged at one side close to the source (401) and the drain (402). The charge carrier mobility of the first active layer (301) is greater than the charge carrier mobility of the second active layer (302). With such a arrangement, the thin film transistor can reduce the leakage current of the thin film transistor while containing a high on-state current.