Abstract : This paper addresses a method to determine firing angles of an unguided ground to ground Multiple Launched Rocket System (MLRS). Six-degree of freedom trajectory simulation is used in prior to reveal all firing ranges of each firing angle and possible scenarios can be categorized. Some firing range can be achieved by two different firing angles while the others can be achieved by only one firing angle. By having prior knowledge of the firing ranges versus the firing angles, and by employing iterative binary search algorithm and six-degree of freedom trajectory calculation, the method to automatically and iteratively search for a firing angle corresponded to a specified firing range is formed. The method is tested with short range and medium range unguided ground to ground rockets at various firing condition. The results are presented and discussed.