The signal polarization fading of N-element DFB laser sensor array demodulated by unbalance fiber Mach-Zehnder interferometer is investigated in this paper. With the Poincare sphere and the optical wave-guide theory,the theoretical model is simplified. Through the theoretical analysis,the expression of visibility lower limit for the minimum visibility of N-element sensor array under optimum control is got. The result of the cyber-simulation experiment testify the expression. At last,the result of cyber-simulation experiment is analyzed.