Transaction processing monitor CICS middleware offers the on-line transaction disposal? and? transaction management as well as the transaction processing environment for business applications. It is suitable for banks which have a large number of emergent on-line transactions.This paper presents a three-tier intermediate business platform based on CICS middleware which can shield the hardwares behind it,and ensures the accurate and reliable data transmission and the integrity of business.It focuses on the design and implementation process of application software system based on CICS,descibing the software framework,modules and technology of the system.