In a dual Mach-Zehnder fiber interferometric sensing system, the high locating accuracy is hardly obtained due to the discrepancy of two detection signals resulting from polarization fading. To keep the stability of the detection signals, a method to control the polarization fading was proposed in this paper. A optical polarization model was established to analyze the origin of polarization fading in the system. It points out that the basic reason for the discrepancy of the detection signal correlation is from that the inconsistency of the polarization characteristics between two sensing fibers results in the effect of the input polarization on detection signals. Based on the analysis, the solutions of controlling the input polarization and searching for the working points of polarization state were put forward to eliminate the polarization fading. Furthermore, the requirements of polarization control were further determined by analyzing the relation between signal correlation coefficients and two parameters of input polarization, and simulated annealing was applied to the verification of this theory. Field test results show that the algorithm can make a fast search for the working points of polarization state, and can maintain a steady signal correlation. It is proved that the polarization fading control method is feasible and effective.