Decoupled parallel xyz positioning stages with a large stroke are desired in high-speed and precise positioning applications. However, currently, such stages either have a short stroke or are unqualified in terms of the parasitic motion and coupling rate. In this paper, a novel flexure-based decoupled parallel xyz positioning stage (FlexDelta) is proposed and its conceptual design, modeling, and experimental investigation are conducted. First, the working principle of FlexDelta is introduced, followed by the design of its mechanism with flexure. Second, the stiffness model of flexure is established using matrix-based Castigliano's second theorem, and the influence of its lateral stiffness on the stiffness model of FlexDelta is comprehensively investigated and then optimally designed. Finally, experiments were conducted using the fabricated prototype. The results reveal that the positioning stage features a centimeter stroke in three axes, with a coupling rate of less than 0.53% and parasitic motion of less than 1.72 mrad over the full range. Its natural frequencies are 20.8 Hz, 20.8 Hz, and 22.4 Hz for the x, y, and z axis, respectively. Multi-axis path-tracking tests were also performed, which validated its dynamic performance with a micrometer error.