A signal transmission method includes: combining a plurality of low-order modulated signals into N modulated signals; and transmitting the N modulated signals on N subcarriers, where the N subcarriers are subcarriers on frequency domain resources of M channels, an nth modulated signal in the N modulated signals is transmitted on an nth subcarrier in the N subcarriers, N is an integer greater than or equal to 2, M is an integer greater than or equal to 2, and n=1, 2, . . . , N. The signal transmission method can improve efficiency of a diversity gain.