Abstract: In experimental modal testing,the choice of number and location of sensors in the structure has major influence on the results.In extreme cases modes may be completely lost,so sensors should be carefully placed.A survey of recent work on sensor placement is given.A three-span prestressed concrete cable-stayed bridge is studied and the optimal placement of sensors on main beam for bridge health monitoring is discussed.The algorithm based on modal assurance criterion as well as the effective independence algorithm are adopted to determine an optimal(or near optimal) sensor placement.Five criteria are used in the former algorithm to assess the suitability of the chosen measurement locations.It is found that the finite element analysis results and the number of targeted modal shapes influence sensor configurations greatly,and the effective independence algorithm gives more ideal results.