In view of the status quo of deployment of large numbers of conventional condition monitoring equipments in current substations， it is pointed out that using communication gateway of condition monitoring is an effective method for conventional condition monitoring equipments to be connected into the new condition monitoring system in smart substations. Based on an analysis of Modbus and IEC 61850， a model mapping approach to Modbus and IEC 61850 is proposed， in which， the object reference of IEC 61850 is mapped onto the address of Modbus， common data class of IEC 61850 is mapped onto the parameter type of Modbus， and abstract communication service of IEC 61850 is mapped onto the protocol data unit of Modbus. An implementation scheme of model mapping by expanding the existing schema file based on system configuration descriptive language is proposed， which can avert ambiguity in information interchange between configuration tools. A model is developed as an instance of condition monitoring for the power capacitor to verify the validity and feasibility of the mapping approach proposed.