The basic principle of heterodyne demodulation of fiber interferometer is introduced. The influence of optical intensity perturbation on heterodyne demodulation based on differential cross-multiply (DCM) and arctangent is researched. Theoretical analysis and numerical simulation are adopted. Theoretical analysis demonstrates that both algorithms can restrain the influence of optical intensity perturbation effectively. But the impact of higher perturbation cannot be eliminated totally, which is limited by the design of lowpass filter. Meanwhile, compared with the traditional phase generated carrier (PGC) demodulation based on arctangent, heterodyne demodulation based on arctangent has an extra advantage in eliminating the influence of the modulation depth C. Numerical simulation matches well with theoretical analysis. Experimental architecture based on heterodyne detection is constructed and demodulation experiment is implemented. The results of experiment demonstrate that both algorithms can eliminate system noise including intensity perturbation.