This paper states the importance of determining the muzzle leaving time of guns with a high degree of accuracy. Two commonly used methods are introduced, which are the high speed photography method and photoelectric transducer method, and the advantage and disadvantage of these two methods are analyzed. Furthermore, a new method to determine the muzzle leaving time of guns based on the combination of high speed photography and synchronized trigger technology is present in this paper, and its principle and uncertainty of measurement are evaluated. The firing experiments shows that the present method has distinguish advantage in accuracy and reliability from other methods. Copyright © 2014 IFSA Publishing, S. L.