There are wrong or insufficient secondary safety measures in secondary equipment maintenance work of smart substation, which will easily lead to power grid accident of relay protection malfunction or refusing to trip. In order to realize error preventing, online monitoring and error proofing alarm for safety measures, this paper firstly analyzes the characteristics of the smart substation secondary maintenance safety measures. Then, the key technologies of safety measures error proofing are expounded in terms of visualization, error proofing mechanism, simulation preview, remote control, and online monitoring. Finally, the application shows that the key technologies can not only prevent the problems of safety measures and ensure correct and reasonable safety measures work, but also realize online monitoring for safety measures process and find safety measures problems in time by error proofing alarm and enhance the level of power grid safe running, which are the technical guarantee for safe production of the large maintenance and large running system. This work is supported by Science and Technology Project of State Grid Jiangsu Electric Power Company (No. J2016082).