Steel composite hollow columns have been studied in order to ease their construction. Welding or bolting are mostly used for connecting the steel tubes of precast steel composite hollow columns. However, welding generally results in temperatures of about 20000 °C in the welding zone and 1300 °C around the welding zone. Thus, the strength of the concrete in regions close to a welding zone is reduced. In this paper, the effects of arc welding and electro-slag welding - two widely used methods for connecting the column modules of steel composite hollow columns - on the temperature change in the welding zone are studied by performing heat transfer analysis. The changes in the strength of the concrete are investigated for each welding method. The rate of decrease in concrete strength due to electro-slag welding was greater than that due to arc welding. In addition, an effective method using ceramic fibres is suggested for preventing strength reduction in concrete due to welding heat.