The Ag3PO4/tetrapod-like ZnO whisker (T-ZnOw) heterostructures were prepared via a simple precipitation method. The obtained heterostructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The photodegradation activity of Ag3PO4/T-ZnOw was evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. When the molar ratio of Ag3PO4 to T-ZnOw was 10% (Ag3PO4/T-ZnOw-2), the highest degradation efficiency (92.9%) could be achieved among the heterostructures. The photodegradation rate constant of Ag3PO4/T-ZnOw-2 (0.05179 min−1) was 3.59 times that of T-ZnOw (0.01444 min−1). Besides, the Ag3PO4/T-ZnOw-2 photocatalyst still possessed a degradation efficiency of 77.8% after four successive cycles. The Ag3PO4/T-ZnOw-2 catalyst had much higher photocatalytic activity than pure T-ZnOw and better stability and reusability than pure Ag3PO4. The effect of different scavengers on degradation efficiency was investigated, and the possible photocatalytic mechanism of the Ag3PO4/T-ZnOw photocatalyst was also put forward.