Disclosed are an organic thin film transistor and a method for preparing the same, an array substrate and a display device. An organic semiconductor layer of the organic thin film transistor is formed on an anisotropic insulating layer, this guarantees that the organic semiconductor layer has a crystallization direction with a high degree of order and the organic semiconductor layer has a specific alignment, thus carrier mobility can be improved, so that the performance of the organic thin film transistor can be upgraded. Moreover, the process of preparing the insulating layer has advantages of simple process, large area and low cost, etc., and the thickness of the anisotropic insulating layer manufactured is small; since there exists no mechanical friction, there exists no badness caused by particles generated by friction.