CAN bus is widely used in distributed control system. ISA is a classic industrial control bus. In order to achieve communication between two buses, design an ISA bus interface to CAN bus conversion circuit and describe the implementation principle of matching and the proposed conversion to be completed to meet the timing conditions. After the analysis of CPLD internal logic analysis, the framework time sequence analysis diagram is given. The result shows that the method is stable and reliable. It can be linked to 30 nodes in the practical applications and has the certain value of engineering.