In recent years, hybrid gas insulated switchgear (HGIS) has been used quite frequently in the construction of UHV bstations in China due to its advantages of moderate cost, small area, safe and reliable operation. The research of distribution of HGIS power frequency electrical field is of great significance for the design and construction of smart substation, the electromagnetic environment assessment and the elimination of unnecessary worries of people about electromagnetic radiation. Traditional charge simulation method (CSM) is too complicated to deal with the problem of complex computing scenarios, this paper proposes a novel method, which combines particle swarm optimization (PSO) with traditional charge simulation method (CSM), to form an optimized PSO-CSM, and applies it to the calculation of power frequency electric field in 500 kV HGIS area. During this process, the influence of main equipment on power frequency electric field and the distribution of power frequency electric field in the whole area are calculated and analyzed, and the relevant suggestions and improvement measures for the protection of power frequency electric field in substation are put forward.