Direct numerical simulation is performed for the wake flow behind an inclined square plate. The hydrodynamic characteristics, including the force coefficients, the three-dimensional vortical structures and vortex shedding process, are presented. Side lengththickness ratio of the square plate is selected as 50. The effects of incidence angle (［0^°，75^°］, 0^° refers to the condition in which the flow is normal to the plate) on the wake transition are discussed. The flow behind the square plate is found to be chaotic at Reynolds number of 300 when the flow is normal to the plate. It is observed that as the incidence angle increases, the flow firstly changes from a chaotic state to a periodic state and finally returns to chaos again at high incidence angles.