In this paper, we present a new system of weak signal detection based on Duffing oscillator with adjustable frequency, in which the frequency of periodic driving force signal can be fixed at a certain value and make the system to be in a same critical chaotic state. Therefore, by adjusting an adjustable signal frequency,the detection system we propose can detect signals of different frequencies in the same critical chaotic state, and overcome the limitation of the previous system which can only detect a signal of a specific frequency in a critical chaotic state. Meanwhile, we analyzed its system performance according to simulation and designed the circuit of the system. Based on the results of simulation and actual condition, we find the system is effective for weak signal detection. We can also find that in the proposed system, the signal detection accuracy increases firstly and then decreases with the increase in amplitude of adjustable signal, while the input noise variance is fixed.In addition, in the improved system, the smaller the variance of the input noise is, the higher the detection accuracy is, and the wider the adjustable operating range is. In this paper, we present a new system of weak signal detection based on Duffing oscillator with adjustable frequency, in which the frequency of periodic driving force signal can be fixed at a certain value and make the system to be in a same critical critical condition. Thus, by adjusting an adjustable signal frequency, the detection system we propose can detect detectable signals of different frequencies in the same critical critical state, and overcome the limitation of the previous system which can only detect a signal of a specific frequency in a critical chaotic state . Meanwhile, we analyzed its system performance according to simulation and designed the circuit of the system. Based on the results of simulation and actual condition, we find the system is effective for weak signal detection. We can also find that in the proposed system, the signal detection accuracy increases first and then decreases with the increase in amplitude of adjustable signal, while the input noise variance is fixed In addition, in the improved system, the smaller the variance of the input noise is, the higher the detection accuracy is, and the wider the adjustable operating range is.