3-Electrode electrochemical toxic gas sensors are more and more widely used in terms of toxic gas detection. This paper presents an ispPAC (in-system programmable Programmable Analog Circuit) -based on 3-electrode toxic gases sensor signal processing circuit designed with software method and implemented with in-system programmable simulators. Then we give a discussion to introducing Programmable Analog Circuit into toxic gases sensor circuits, can further increase system reliability, stability, sensitivity and integration degree, and enhance flexibility of system design.