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 r j and a phase angle ϕ y of a receive signal, an amplitude r x j and a phase angle ϕ x j of each constellation point x j in a decision constellation point set, and a standard deviation σ n of Gaussian noise and a standard deviation σ θ of phase noise; calculating, according to the symbol probability parameter, a symbol probability that a transmit signal is each constellation point x j 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.