Measurement difficulties and physical complexities for mathematical modeling’s caused to numerical simulation assumed as the most suitable way to  study flow field and heat transfer in electric arc furnace. Harmful gas from NOx family in electric arc furnace result to acidic rains and fog. Investigations show that NOx production mainly extracted from Zeldowich and thermal mechanisms which formed in the period of slag removal from the furnace. The main reasons for such a phenomena are high temperature and presence of Oxygen and nitrogen in air penetrated to the furnace when the furnace door is opened .The present study includes a 3D modeling of the flow field and heat transfer to simulate electric arc furnace when the door is opened and in period of slag removal.  The air flow is carefully studied In furnace and door type and Nox formation studied where door position and type are changed. Results show that door type is not so important in NOx formation but the best location to reduce NOx content is the place in opposite of outlet elbow for dedusting facility.