The photocatalytic performance of Ag3PO4 is severely restricted by the photocorrosion and high charge carrier recombination rate. In order to overcome these defects, a novel Ag3PO4/calcined Zn-Al layered double hydroxides (APMO) heterostructure photocatalyst was fabricated via in-situ growth of Ag3PO4 particles on the surface of calcined Zn-Al layered double hydroxides (MMO). The crystal structures, morphologies, optical and photo-electrochemical properties of the as-synthesized samples were characterized using various techniques, and its photocatalytic activity for tetracycline (TC) degradation was evaluated under simulated solar light irradiation. Obviously, all the APMO composites demonstrated much higher photocatalytic performances for TC degradation than pure Ag3PO4. Especially, the APMO70 showed the highest photocatalytic activity, which was almost about 49.3 times as high as that of pure Ag3PO4, and the degradation efficiency was still above 89% after 5 cycles. The improved photocatalytic performance and stability of APMO were ascribed to the efficient charge transfer and strong interfacial contact between Ag3PO4 and MMO. The possible photocatalytic mechanisms involving the charge transfer pathway and reactive species generation during the process of TC degradation were also discussed. Finally, the aquatic toxicity of TC was assessed using Chlorella vulgaris (C. vulgaris) as an ecological indicator, and the result suggested that the as-prepared APMO composite can effectively diminish the aquatic toxicity of TC.