Abstract: Based on heat transfer theory, the similarity theory of temperature field focusing on light steel members (structures) under fire is researched, and the simplified furnace temperature curves are proposed and proved by numerical and experimental methods. Meanwhile, the factors that influence the similarity theory of temperature field focusing on light steel members (structures) with or without non-bulgy fire retardant coating are compared. The results show that the temperature of experimental models under the simplified furnace temperature curves with time similarity constant "1" s basically the same as that of prototype structures under the standard ISO834 temperature curve. This implies that the similarity theory of temperature field focusing on light steel members (structures) under fire is valid. Furnace temperature curves are negatively correlated with steel density and specific heat, and positively correlated with specific surface area and size similarity constant. For light steel members (structures) with non-bulgy fire retardant coating, they are also negatively correlated with coating thermal resistance, and positively correlated with the coating thickness similarity constant.