The construction of a heterojunction photocatalyst as an effective method to enhance the charge separation has attracted great attention from researchers. Herein, a novel BiVO4/self-assembled perylene diimide (BiVO4/PDIsa) organic supermolecule photocatalyst was successfully constructed via an in situ electrostatic assembling method. Various characterization methods were employed to systematically study the phase structure, morphology, and photoelectrochemical properties of BiVO4/PDIsa. Among the different ratios of composites, the 20%BiVO4/PDIsa exhibited the optimal photocatalytic activity under visible-light irradiation, and its degradation efficiency for tetracycline (TC) could reach 81.75% within 30 min. In addition, the corresponding TC degradation rate constant was 0.0545 min-1, which was 1.69 times and 3.61 times that of the pure PDIsa and BiVO4, respectively. Subsequently, the radical trapping experiments and electron spin response (ESR) test indicated that 1O2, •O2-, and h+ were the primary reactive species in the photocatalytic process. Importantly, the efficient electron migration path and photocatalytic mechanism of the catalyst were inferred by experimental study and density functional theory (DFT) calculations. In brief, this work provides a promising approach in designing an inorganic-organic Z-scheme heterojunction photocatalyst for environmental remediation.