A control method of a handheld electronic device with a touch panel is provided. The control method includes the following steps. Firstly, a user interface is displayed by the touch panel, where the user interface includes a sensing area corresponding to a predefined function. Then, an adjusting function for the sensing area is enabled. Afterward, it is determined whether the sensing area receives an adjusting instruction or not, and when the sensing area receives the adjusting instruction, the sensing area is adjusted according to the adjusting instruction and the size change process is continuously presented on the touch panel. The adjusted sensing area still corresponds to the predefined function.