Revealing the design and synthesis of precisely tailored crystalline catalysts for achieving efficient photocatalytic conversion of styrene into high-value-added products remains a challenging task. In this work, a highly stable crystalline polyoxovanadate functionalized by the dl-tartaric acid ligand H2[V4O4(H2O)6(tart)2]·H2O [1, tart = C4H2O6] was successfully synthesized by conventional aqueous solution methods. The photocatalytic performance was evaluated for the photosynthesis of styrene oxide by employing an oxygen source as the oxidant in the visible light (>420 nm) conditions at room temperature with compound 1 as a heterogeneous catalyst. Furthermore, compound 1 manifested accomplished stability and reusability, maintaining a high reaction activity even after three consecutive reaction cycles. This paper not only contributes to broadening the structural diversity of polyoxovanadate but also sheds new light on green catalytic conversion.