The application of structural health monitoring system in helicopters is still at preliminary stage, and one of the reasons is the difficulty to assess the economic benefits before its application. As a complex system, helicopter has more than two performance levels, and the binary reliability theory cannot accurately describe the state of its structure. In this regard, this paper proposes a multi-state economy quantification method for structural health monitoring system, which integrates the Bayesian-based value of information theory. Considering the multi-state characteristic of helicopter blades, a framework is developed to access multi-state probabilistic model based on crack propagation theory and Monte Carlo simulation methods. Subsequently, a Bayesian decision-making method for quantifying economic value of monitoring information of helicopter blades was constructed. The structural state is probabilistically characterized and updated by using vibration monitoring information and Bayesian theory. Finally, taking the French dolphin blade maintenance as an example, the economics of the vibration-based helicopter monitoring system was quantified.