With wide application of IEC 61850 based communication network in digital substation， implementation of remote test of relay protection in digital substation has shown the technical feasibility and economic necessity. The design to realize remote test is proposed， by setting up a dedicated remote test control unit（RTCU） at substation bay level and modernization of the merging unit（MU）， which has been simulated in laboratory experiments. Finally， the suggestions on the application step of remote test are proposed.