The scheme of secondary equipment outdoor layout in smart substation has become the development trend in constructing smart substation.Some schemes about out-door layout relay protection in smart substation using electronic transformer is provided and compared,which is mainly focused on technical ideas,implementation plan and their advantages and disadvantages in engineering application.In addition,aiming at the problem of changing in testing,operation and maintenance work under this new mode,a brief introduction is provided on assembly line automatically closed loop test technology of outdoor layout,miniaturization relay protection equipment.The research results have been initially applied in design,test,operation and maintenance work in smart substation.