Abstract: Based on a great deal of statistics and with regression analysis,discussions are made on the law of chemical composition change of 20G,15CrMoG and 12Cr1MoVG steels for hi-pressure boiler tube-making before and after electroslag remelting.As a result,the approximation equation for computing the chemical content change of the said steels before and after electroslag remelting is derived.With this approximation equation the control range of the chemical composition of the consumable electrode can be determined.