The invention discloses a method and a device for adjusting the Wireless-Fidelity (Wi-Fi) transmission power and a terminal, relates to the technical field of information, and can reduce the power consumption of a Wi-Fi module in the terminal to save the electricity of the terminal. The method comprises the following steps: when connected with a wireless access point, the terminal determines an initial value of the Wi-Fi transmission power at first, then receives a signal transmitted by the wireless access point in real time, determines a received signal strength indicator (RSSI) and judges whether a range where the RSSI is positioned is changed; if the range where the RSSI is positioned is not changed, the terminal determines the current packet loss rate, and judges whether the current packet loss rate is less than a preset packet loss rate threshold value; and finally, if the current packet loss rate is less than the preset packet loss rate threshold value, the terminal reduces the Wi-Fi transmission power. The method is applicable to being used by the terminal for adjusting the Wi-Fi transmission power according to the RSSI and the packet loss rate.