Sensitivity is a crucial performance parameter for hydrogels, as it significantly affects their application in flexible devices. To address the problem of the low sensitivity of polyvinyl alcohol (PVA) hydrogels, we designed and prepared a PVA hydrogel with a small waist structure whose Gaussian curvature is negative. It was found that the small-waist structure greatly increased the deformation of the PVA hydrogel with a negative Poisson’s ratio behavior upon compression, and its sensitivity was 6.1 times that of the hydrogel in the conventional cylindrical shape, which was highly favorable for the improvement in the sensitivity of the PVA hydrogel. Moreover, the small waist structured PVA hydrogel was assembled into a 3×3 matrix flexible pressure sensing device, which was capable of precisely detecting the position of space pressure.