Due to the turning on or off operation of the circuit breakers and the disconnected switches, a strong electromagnetic interference in gas-insulated substations (GIS) is commonly generated. The transient wave process with a very wide frequency range can generate the transient electromagnetic field from the connector between the GIS crust and the high-voltage cable. The software TEMFGIS is provided to predict the transient electromagnetic field in GIS by using MATLAB. Its validity is verified by the measurement results