Recently, interest for environmental pollution in various fields is on the increase, and the researches on the life cycle assessment of environmental performance assessment method for calculating the environmental loads are currently mose performed. In this study, we build the data for 204 of steel bridge designed after 2000 year, and the 120 of bridge which were selected to from obtained results were calculated the environmental loads at the planning stage based on the life cycle assessment. Based on this, the environmental load estimation model was developed by using case-based reasoning. This study in future is renewing the DB of the environmental load model cases based on the developed model from this study , and is improving the accuracy of the developed models by adding an additional analysis of new cases.