Access control system is an important part of the prison security. The stable operation of access controller is the premise of reliable work of an access control system. For this reason, reliability model in series and reliability principle of access controller circuit design are firstly analyzed. In additional,,access control system hardware circuit is designed., including part of the reliability circuit of processor modules, memory modules, I/O modules, other unit module. Experimental results show that designed access control system can reliably and correctly work.