The subject of this dissertation is production planning in steel industry with two approaches of optimization models, and also processes of business and performance evaluation indexes. Among production planning problems in steel industry on the basis of make to order environment, the problems of order acceptance and order planning were formulated and solved through decomposition approach and by presenting exact/heuristic algorithms. In formulating the problems, all important and effective operational constraints were considered in order to keep the practical feature of the models. In the order planning model, in contrast to previous studies, the model is designed to not only consider common constraints of capacity and delivery date considerations, but also the important and effective operational constraints of the production lines. This has been due to the importance of coming to applicable programs and plans. Solving operational problems of the time horizon of several weeks (huge-dimensional problems) in an acceptable time were the most important challenges of modeling and proposing solutions. In the process approach by applying the standard model of SCOR the necessary processes in the operational level and in the scope of order acceptance and order planning problems were defined. Also, the performance evaluation indexes were defined and formulated. The proposed models were executed on the data gathered from Mobarakeh Steel Factory. Numerical results have been presented which show considerable improvement in the defined indexes.