An air-insulated sealing switch cabinet with a side expansion device comprises a first cabinet body and a second cabinet body. The first cabinet body and the second cabinet body are provided with openwindows used for expansion, and an insulation partition plate is arranged between two adjacent copper bars of the first cabinet body and the second cabinet body. The copper bar of the first cabinet body or the second cabinet body is provided with a cabinet combination expansion contact claw used for overlapping the copper bar. Each positioning reinforcing plate strip of the first cabinet body orthe second cabinet body is provided with an annular sealing component. The first cabinet body and the second cabinet body are provided with connecting plates, and each positioning reinforcing plate strip of the combined first cabinet body and second cabinet body abuts against and makes contact with the annular sealing component to form sealing. The switch cabinet has advantages of low cost, good sealing performance and low requirements of an installation environment and combination port positions. A large-window type is adopted, a high-insulation-performance phase partition plate and a self-adaptive cabinet combination expansion contact claw structure are combined, and accuracy, flexibility and reliability of switch cabinet side expansion and combination are greatly increased.