An implementation of dual CPU(central processing unit) redundant control based on DeviceNet field bus was introduced. Dual CPU redundant design played an important role to improve the DCS(distributed computer system) reliability. In the implementation, two CPU units and some data I/O(input/output) units were connected through a DeviceNet field bus, and DeviceNet client/server programs running in the CPU units implemented the data synchronization between the two CPU units as well as the redundant control over data I/O units. When the main CPU unit encountered some serious errors and broke down, a fake DeviceNet group 2 only client program running on the backup CPU unit helped to fast switching, and therefore the backup [JP2]CPU unit took over the control of the whole system in less than 8 milliseconds. This design was put into practice in the design for process control stations of a special DCS system and improved the system reliability.