Abstract: Taking a typical power supply system of deep well as an example,the paper introduced design of a calculation software for relay protection setting of coal mine power grid.The software takes each switch cabinet as setting part to do setting calculation and can realize setting calculation of each switch cabinet by modifying a few parameters,which is simple and practical.It adopts VB program language and SQL Server 2000 database as developing tools so that its development and maintenance are easy and it has strong management function.The software has good man-machine interface and functions of data input,query,modification and print output,which has easy operation and strong adjustability, and improves accuracy of setting values of relay protection of coal mine power grid and running management level of relay protection system.