A method and a device for processing a window task are provided. The method includes: creating a thread class including a first member variable for representing whether a task processed currently has been cancelled and a first member function for initiating a backstage thread; creating a backstage thread object based on the thread class when a task that takes time needs to be processed, and initializing the first member variable in the backstage thread object as FALSE, invoking the first member function in the backstage thread object to initiate the backstage thread; in process of the backstage thread processing the task that takes time, if a close instruction for a current window is received, setting the first member variable in the backstage thread object as TRUE to release the memory space occupied by the backstage thread object and closing the current window.