In order to solve the problem of optimum sensor placement in the damage detection of complex structures, this paper presents a multi-objective optimum sensor placement method (MO-OSP). An integrated information matrix was deduced from the structural motion equation, which includes information on mode independence, damage sensitivity and modal strain energy. Based on the information entropy, an objective function was set up with the criterion of maximum norm of the information matrix and minimum condition number of the sensitivity matrix, and then the sensors optimization was carried out. The improved MO-OSP method was compared with three typical optimal sensor placement methods in terms of several evaluation criteria based on damage tests on the launch platform. Numerical example analyses showed that the improved method could not only ensure the linear independence of mode shapes and damage sensitivity, but also had outstanding robustness, thus making it an ideal method for solving the problem of optimum sensor placement in the damage detection of complex structures.