The liquid level sensor is widely used. The simulation of the liquid level sensor signal is beneficial to the design of the signal acquisition circuit of the liquid level sensor. This paper proposed an active adjustable capacitor built by operational amplifier in order to simulate the output characteristics of the liquid level sensor by controlling the charge and discharge process. In this paper, the conditioning circuit is designed. The measured capacitance in two conventional capacitance measurement schemes is simulated. The feasibility of the scheme is theoretically analyzed. In the simulation test for 20pF~300pF capacitor, the simulation accuracy reaches 0.2pF, the step length is 0.04pF. The precision is better than the passive adjustable capacitor. The scheme has certain engineering application prospects.