To investigate the effects of restrictive ventilation conditions in a covered vertical shaft on air-pocket motion and geyser characteristics, a combined approach of physical model tests and numerical simulations was employed to systematically examine the influences of shaft diameter, ventilation ratio, external head, and initial air-pocket volume on air-pocket motion and geyser occurrence. The results show that the water-level rise in the shaft during air-pocket release can be divided into an air-pocket-driven stage and a pressure-difference-driven stage, resulting in four typical flow regimes: no geyser, an air-pocket-driven geyser only, a pressure-difference-driven geyser only, and both an air-pocket-driven geyser and a pressure-difference-driven geyser. The air-pocket morphology is jointly influenced by the shaft-to-pipe diameter ratio, ventilation ratio, and air-pocket length. In small-diameter shafts, the air pocket tends to be symmetric and intrudes into the upstream pipe, whereas in larger-diameter shafts, the air pocket exhibits significant asymmetry and remains trapped in the downstream pipe. For small-diameter shafts, the air-pocket head morphology varies non-monotonically with the ventilation ratio: it is approximately symmetric at a ventilation ratio of 0, becomes irregular at ventilation ratios of 0.01 and 0.02, returns to a nearly symmetric shape at ventilation ratios of 0.05 and 0.1, and develops into a sharply asymmetric shape inclined toward the downstream direction at a ventilation ratio of 1 (fully ventilated condition). A larger air-pocket length results in stronger disturbances to the free surface and a higher release position. The rising velocities of both the air-pocket head and the free surface increase significantly with increasing ventilation ratio, external head, and air-pocket length, and decrease with increasing shaft diameter.