The present invention discloses an array substrate and a preparation method thereof, a display panel and a display device, so as to solve the problem that the performance of the oxide TFT may be reduced and even out of work due to relatively great shift of the threshold voltage of the oxide TFT since the water, oxygen and hydrogen groups may permeate to the active layer of the oxide TFT from the passivation layer above the oxide TFT. The array substrate comprises a base substrate, an oxide thin film transistor TFT formed on the base substrate, a passivation layer being arranged above the oxide TFT, the passivation layer comprises a first film layer, the first film layer being a silicon oxide film; the passivation further comprises a second film layer formed on the first film layer, the second film layer is an alternate stack of silicon nitride films and silicon oxide films, a base layer of the second film layer close to the first film layer is a silicon nitride film; wherein the thickness of the first film layer is greater than the thickness of the second film layer.