This paper presents structure, characteristic and condition of microprocessor based relay communication system. A available start network configuration for the system is put forward. Message manager is used in the net. Some problems appearing in serial communication of field unit are also discussed. A way is brought forward for the communication system, which is an application of PTS function of 80C196KC SCM. The order is proposed for the PTS's one transmission model, which is the data longness must be destined in the net message agreement. A data redundance technic is adopted for improved message dependability.