The air flow field plays a key role in melt blowing. In this article, an optimal design procedure that improves the airflow field of melt blowing is proposed. A parameter, stagnation temperature which is a combination of static temperature and kinetic temperature, is proposed to evaluate the air flow field. The stagnation temperature is obtained via computer simulation, while optimization is accomplished by genetic algorithm. Four main geometry parameters of the slot die: slot width, nose piece width, slot angle, and setback are investigated. The optimal results were achieved in the 40th generation. The results also show that the smaller slot angle and larger slot width can result in the higher stagnation temperature. (C) 2009 Wiley Periodicals, Inc. I Appl Polym Sci 115: 1540-1545, 2010