Most of the steel structures are constructed in separated modules which will be loaded out and assembled together on the field. The dimension of the modules will directly affect whether they can be fitted up successfully. So it is important to take strictly dimension control to meet the specification which is usually in mm. The characteristic of Thermal Expansion and Contraction of steel will have significant effect on module dimension during the long construction period as well as the large temperature span. Based on the modules with different size, the dimension under different temperature was measured and recorded. The variation of dimension and the temperature was analyzed. Meanwhile, a thermal correction model was taken into account. The study shows that temperature has remarkable influence on module dimension, and the mathematical model can be used for the thermal correction.