Vascular plaque deformation reduces blood flow, increases arterial embolism risk, and may lead to ischemic stroke. Plaque stiffness varies widely and is an important factor influencing both plaque and parent artery deformation. These geometric changes affect local hemodynamics, which impact plaque initiation influencing disease progression. However, most previous studies used non-elastic stenotic vessel models. For more realistic analysis, we constructed a stenosis model comprising an elastic poly (vinyl alcohol) hydrogel (PVA-H) parent artery and plaque of variable stiffness. Our previous study using this flexible model demonstrated substantial effects of hydrostatic pressure. Here ultrasonography was conducted under changing hydrostatic pressure to measure geometric changes at the narrowest cross section. PVA-H specimens were constructed with the stiffness of a hard lipid core, smooth muscle, and plaque, as estimated by tensile tests using 5, 12, and 15 wt% PVA, respectively. The change in cross-sectional aspect ratio (height/face length) at the narrowest site is largest (~1.3) for the 5 wt% PVA-H plaque and smallest (~1.2) for the 12 wt% PVA-H plaque. Stenotic artery deformation depends on both artery and plaque elasticity. Hydrostatic pressure has a substantial effect on both vessel and plaque geometries, which markedly alter blood flow.