The present invention provides a communication system comprising a host computer, control cabinets and peripheral devices, the control cabinets comprising serial ports used for communication among the peripheral devices and the host computer. The operating period of the communication system includes a polling phase and a free communication phase, in the polling phase the host computer sends query instructions to the control cabinets through the serial ports on each of the control cabinets, and in the free communication phase the control cabinets communicate with corresponding peripheral devices through the serial ports. The present invention also provides a communication method for the communication system. Using the communication system of the present invention, reliability of communication among the control cabinets, the host computer and the peripheral devices through a same serial port can be ensured without increasing hardware volume and costs of the communication system.