Abstract: Modern forms of warfare have posed increasingly higher requirements on the precision of small-caliber rapid-fire weapons, while the issue of shooting anomalies, resulting from elevated barrel temperature, is in existence all through. To handle the aforementioned issues, the muzzle motion behavior under heated barrel conditions was analyzed in this paper. Taking the 5.8 mm rifle as research object, a thermo-pressure coupled model of bullet-barrel interaction was constructed based on the nonlinear finite element method. Some tests were carried out to validate the correctness of the coupled model on bullet muzzle velocity and bullet soft-recovery. Based on this, the study summarized the impact of material thermos-physical properties on the muzzle motion state under heated barrel conditions. Specifically, the influence was analyzed from three distinct aspects, the thermoplastic behavior of the bullet jacket, the thermo-elastic response of the barrel, and the thermal expansion characteristics of the barrel. The results show that the constructed model can be provided for the resolution of shooting anomalies resulting from elevated barrel temperature and for the study of the mechanism of bullet/barrel interaction.