An embodiment of the present invention discloses a Wi-Fi device, including a radio frequency circuit, a signal processor, an application processor, and a Wi-Fi chip. The application processor is configured to preset the work mode of the Wi-Fi chip to a single input single output SISO mode, and is further configured to acquire a value of a parameter of an uplink wireless network, and when the value of the parameter of the uplink wireless network is determined to be greater than or equal to a preset value, set the work mode of the Wi-Fi chip to a multiple-input multiple-output MIMO mode. An embodiment of the present invention further discloses a method for setting a communications mode.