In the fiber optical sensor demodulation based on asymmetric 3×3 coupler, the fiber-optic median phase shift 3×3 adder due to the limitation of the manufacturing process and the susceptibility to external environmental interference, and then the three-way signal output has an uneven splitting ratio and an asymmetric phenomenon that the phase difference cannot meet 120°, which causes a problem that could not be accurately corrected. In order to solve these problems, a new 3×3 replacer was used, and theoretical analysis and experimental verification were performed. The mean two algorithms were used to pre-process any two signals output, and compressed the original three signals. The power and phase difference between the output signals of the two channels make the new three-channel signals after correction to be approximately symmetrical output, and then perform a symmetric algorithm operation. Simulation and experimental results show that the new scheme can effectively correct the asymmetry of the three output signals of the positive 3×3 converter, and classify it. Noise level of the new scheme is about 10-4mW and signal-to-noise ratio is about 50dB. Compared with the traditional alternative scheme, the new structure can obtain higher accuracy and signal-to-noise ratio of the signal under test. In addition, according to the simulation and experimental results, the symmetry conditions of the output of the replacer and the anti-noise capability of the new superposition scheme are analyzed. The result has a good guiding role in the field of optical fiber polarizers and accelerates the practical process of optical fiber sensing technology.