Mechanical time (MT) fuzes activate the flare or smoke grenade at a desired point by setting the predetermined length of time before firing. The performance of the MT fuze is evaluated by determining whether it operates at an appropriate location, hence, it is highly required to measure the function time of the fuze accurately. Seohwa area, where the firing test takes place, is a mountainous terrain, and the conventional measurement of function time of MT fuzes has relatively low level of test reliability due to human error. In this study, the reliability of such a measurement method is improved by applying the image analysis. The firing test data have been acquired using the improved measurement method, and these data are analyzed and compared with the conventional method. As a result, function time difference of more than 0.3 seconds in average has been confirmed, which can increase the reliability of test and evaluation.