The present invention provides a signal demodulation method and device. The method includes: obtaining a symbol probability parameter, where the symbol probability parameter comprises: an amplitude ry and a phase angle φy of a receive signal, an amplitude rxj and a phase angle φxj of each constellation point xj in a decision constellation point set, and a standard deviation σn of Gaussian noise and a standard deviation πθ of phase noise; calculating, according to the symbol probability parameter, a symbol probability that a transmit signal is each constellation point xj in the decision constellation point set; and performing demodulation according to the symbol probability, and outputting demodulation information. The present invention improves an anti-phase-noise capability.