The sensor system, especially the sensor placement, plays an importance part in the research of the health monitoring system of large-span cable-stayed bridge. The various optimum algorithms for the sensor placement at present are classified and discussed. Genetic algorithm is introduced and applied to determining the optimal position of the sensors of the monitoring system of the single-tower cable-stayed bridge of the Zhaobaoshan in Ningbo. Numerical simulation results indicates that this algorithm has a good convergence and ability to get the stable and reliable solution.