Conductive contact point overheating is the main failure mode of High-Voltage(HV) switchgear cabinet, therefore a low cost real time in-situ on-line contact point temperature monitoring system, which plays as the early failure warning system, has become very important to safeguard reliable operation of such HV devices. Before the system design, the electromagnetic environment in the cabinet must be understood well. Instanced by KYN28-12(Z) type HV switchgear, a 3-D numerical simulation model for electromagnetic field in the HV switchgear cabinet was established with AC/DC module of COMSOL Multiphysics. With the Quasi-Statics electromagnetic analytical method provided by the software, 3-D electromagnetic field distribution and its intensity in the HV switchgear cabinet were obtained under the standard working condition, i.e. 12 kV@50 Hz AC voltage applied to each phase line. The 3-D electromagnetic numerical simulation result showed that at the corners of the rectangular phase line, both electric intensity and magnetic intensity reached their maximum values. It also showed that the electromagnetic intensity was lower between two phase lines.