The present application provides a method and a device for preventing window's lagging, and relates to the field of computer technology. The method comprises: when a child window is created by a thread, a middle window being firstly created in a thread different from the thread in which each child window of a window system is positioned, wherein the middle window is the parent window of the child window currently created, the parent window of the middle window is a frame parent window, and the thread in which the child window currently created is positioned differs from the thread in which the frame parent window is positioned; if window's lagging of a child window occurs, a window's lagging message of the child window in which window's lagging occurs being sent to the thread in which the corresponding middle window is positioned; and the middle window and the child window in which window's lagging occurs are separated from a window frame by the thread in which the middle window is positioned. By the present application, the middle window corresponding to the child window in which window's lagging occurs can be separated from the window system; the window's lagging state of the integral window system caused by the window's lagging of the child window is avoided; and the window's lagging problem of the integral window system caused by the window's lagging of the child window in the windows system of the Windows is solved.