This paper expounds the development of the microcomputer-based protection in China and some problems that are appeared at present. The miniaturization and outdoor installation of relay protection are proposed. The secondary system architecture of substation, smart management unit and outdoor installation operation box are studied in detail. The expected target of unprotected outdoor installation is listed:by outdoor installed locally to reduce intermediate links to increase rapidity, reliability and avoid the interference; through the plug and play, shorten the maintenance time, improve maintenance efficiency; promote the optimization of smart substation secondary system design scheme and the innovation of the operation and maintenance technology and management to make substation safe, reliable, convenient operation and maintenance, energy saving, environmental protection, and economic. Technical conditions for unprotected outdoor installation are mature, and outdoor installation line protection and outdoor installation distributed bus protection have experienced the test of practice, and outdoor installation relay protection will open a new model of substation construction, operation and maintenance.