In order to fulfill the standardization design and engineering application for distributed protection functions based on IEC 61850， the interaction relations among intelligent electrical devices（IEDs） and different logical nodes（LNs） under the protection functions need to be described strictly. A unified function model is proposed for the interaction process of IED and the interaction modes among IEDs and LNs are expatiated. The extended collaborative and sequence diagrams are studied to embody the cooperative association and time sequence among LNs under the distributed protections. At last， the software architecture of IED is designed. The interaction model may give a reference for the interoperating tests.