Embodiments provide a transmit power determining method. Under this method, a first wireless communications device determines its distance to a second wireless communications device a working frequency of the second wireless communications device, and a first condition is met. If the first wireless communications device determines that its maximum transmit power is greater than a preset threshold, it adjusts the maximum transmit power, so that the adjusted maximum transmit power is equal to or less than the preset threshold. The preset threshold is used to suppress interference caused by the first wireless communications device to receiving performance of the second wireless communications device under the first condition. The first condition includes the distance to the second wireless communications device being less than or equal to a first threshold, and a working frequency difference between the first and second wireless communications devices being less than or equal to a second threshold.