In order to study the flame propagation characteristics of a ethylene/polyethylene hybrid explosion under pressure accumulation, a visual pressure-bearing gas/power hybrid-explosion experimental platform was built. The flame propagation characteristics of polyethylene and ethylene/polyethylene hybrid explosions in the closed vessel were analyzed. The results show that the flame brightness, flame front continuity and average flame propagation velocity of polyethylene dust explosion in the closed vessel increased first and then decreased when the polyethylene dust concentration increased. The curve of the flame propagation velocity with time had obvious pulsation characteristics. Adding 1% and 3% ethylene to different concentrations of polyethylene dust significantly improved its explosion flame brightness, flame front continuity and average flame propagation velocity. Moreover, it also improved the fluctuation amplitude of the explosion flame propagation velocity with time curve. The explosion flame of the polyethylene dust and ethylene/polyethylene hybrid mixture included four zones during the propagation process, which were denoted as the unburned zone, preheated zone, premixed flame zone and dust flame zone. The addition of ethylene to polyethylene dust can significantly increase its thickness of premixed flame zone and preheated zone, and the thickness increased when the ethylene concentration increased.