A wireless network device has a signal detection function and a switching method for the same. A wireless network signal detection module is installed in the wireless network device, and is switched to a wireless network interface card mode or a wireless network signal detection mode after the voltage regulator in the device determines the load voltage. So that the versatile wireless network device is formed to detect the wireless network signal without the PC's help. The steps of switching to the signal detection mode are inclusively detecting the load voltage, switching to the wireless network signal detection mode, scanning the wireless network signal, and finally showing a result in a plurality of manners.