Manufacturing industries face to the market where unexpected number of product is required in short delivery time. Therefore, a production plan with forecast is much important to meet the customer demand as well as low-level inventory management. This paper shows a method to allocate a portion of the production plan to each customer order effectively and efficiently. The numerical model has an objective function minimizing both inventory const and delivery lateness. Since, each order has individual priority and constraints, Lagrangian Decomposition and Coordination (LDC) method is used to get a semi-optimal solution.