Public administration is a new social administrating mode based on ethic relationship,in which there is a balanceable interaction of power relation,law relation and ethic relation. Power and law relations are inherited from the past social administrating mode,while ethic relation is the unique professional relation in public administrating relationship. The objective basis of the public administrating ethic is the expectation for social service,while its subjective basis is moral consciousness of public administrators. The historical process of human equality is the key to understanding the historical inevitability for the being of public administrating ethic relationship.