This Recommendation specifies the calculating methods for dangerous effects, tolerable limits of dangerous effects, tolerable limits of electromagnetic effects from high-voltage substation, distance requirement and protection methods, protective measures, as well as requirements of power frequency magnetic field immunity of server when an IDC is co-sited with a high-voltage substation. The co-sites of IDC and high-voltage substation discussed in this Recommendation include proximity, co-earthing network, and co-building room. This Recommendation is applicable to IDCs and large communication centres co-sited with high-voltage substations. For small internet data site, this Recommendation may not be applicable.