In this paper,high-level Rossler chaotic oscillator and proportional differential control are used together to detect the frequency of weak signal.Rossler system is controlled to critical state from periodic state to chaotic state.Then the unknown signal is put into the Rossler system.Proportional differential control is used to regulate the system to periodic state and the method of spectrum analysis is employed to detect the frequency the unknown signal.The presented method exhibits higher detection precision and is simpler than Duffing equation which needs many chaotic oscillators.Numerical simulation verifies that the presented method is feasible.