The invention discloses a key generation method and a device applying the method to solve the problem that the key generation method cannot simultaneously achieve high key consistency and key entropy in the prior art. The method is used for generating a key of an OFDM-TDD (orthogonal frequency division multiplexing-time division duplex) communication system and includes the steps: estimating a first channel and a second channel of the communication system to obtain first channel state information and second channel state information; judging whether target channel state information exists or not according to phases and amplitudes of the first channel state information and the second channel state information; acquiring the key of the communication system according to the target channel state information. The key generation method and the device acquire the key by combined utilization of the channel amplitudes and phase information, and overcome the shortcomings of low key entropy due to acquiring the key by individually utilizing the channel amplitudes and poor key consistency due to acquiring the key by individually utilizing the channel phases, so that both key consistency and key entropy are high.