This paper is a study on the compositional change of steel sheet according to the heating temperature using portable XRF. Color coating galvanized iron (CCGI), galvanized iron (GI), galvalume steel (GL), and electrolytic galvanized iron (EGI) often used in prefabricated buildings and interior design are selected as test samples, and the steel sheet is heated using a sand burner for 1800 s. According to the method, the compositional change of the steel sheet was measured and analyzed. As a result of the experiment, in the case of samples oxidized for 1 day after non-watering, the components with low melting points such as Zn and Al decreased according to the heating temperature of the steel sheet, and therefore the components of Fe with relatively high melting points increased high. In the case of the sample oxidized for 7 days after watering, the steel sheet damaged by the heating temperature reacted with water and the Fe component was measured to be higher. The possibility of predicting the heating temperature of the steel sheet through the change of the composition ratio of constituent elements was confirmed when portable XRF was used for fire investigation.