During the long-term operation, anti-aircraft missile weapons are characterized by the technical condition and level of reliability change influeincing the efficiency on the intended use. The article presents a model of surface-to-air missile system (SAMS) reliability during long-term operation, which contains a set of models, namely: a model of operation of ground combat assets (GCA) of SAMS according to the typical cyclogram of intended use (TCIU); a reliability dynamics model of SAMS GCA in the established system of maintenance and repair (SMR) and a reliability dynamics model of surface-to-air missiles (SAM) during extended usage. It is expedient to use the developed model at substantiation of requirements to the indicators of SAMS and SAM reliability for their development or modernization; when developing SAMS repair plans in terms of determining the time of SAMS GCA and (or) SAM repairing time and when developing methods for assessing the effectiveness of SAMS taking into account the duration of SAMS GCA and SAMS usage.