The design of insulation structures and the distribution of electric fields in switchgear operating under complex conditions, such as humidity and condensation, significantly influence the operational reliability of the switchgear. This paper focuses on 10 kV air insulated switchgear as the research subject. It conducts electrical performance testing of insulation materials used in switchgear, obtained the dielectric properties and power frequency breakdown strength of epoxy silicon oxide composite insulation materials. It establishes a refined model of 10 kV air-insulated switchgear, and simulates and analyzes the electric field distribution of key components, including insulators, bushings, and contact boxes, under power frequency withstand voltage. Additionally, it investigates the impact of defects, such as condensation, on the electric field distribution of insulation components in switchgear. The purpose of this paper is to accurately understand the electric field distribution patterns of critical insulation structures in switchgear. The findings can provide a basis for calculations and analyses related to the structural design and fault diagnosis of switchgear insulation components.