Antifungal activity of petroleum ether extract ofPsoralea corylifoliaL. seed, tested againstFusariumsp. namely,Fusarium oxysporum, Fusarium moniliforme,andFusarium graminearum, was evaluated by agar well diffusion assay. The chromatographic fractionation of the extract yielded a new phenyl derivative of pyranocoumarin (PDP). The structure of the PDP was confirmed using spectroscopic characterization (GC-MS, IR, and NMR), and a molecular mass ofm/z414 [M-2H]+with molecular formula C27H28O4was obtained. The PDP had a potent antifungal activity with a minimum inhibitory concentration of 1 mg/mL againstFusariumsp. Molecular docking using Grid-Based Ligand Docking with Energetics (GLIDE, Schrodinger) was carried out with the Tri101, trichothecene 3-O-acetyltransferase, as target protein to propose a mechanism for the antifungal activity. The ligand PDP showed bifurcated hydrogen bond interaction with active site residues at TYR 413 and a single hydrogen bond interaction at ARG 402 with a docking score −7.19 and glide energy of −45.78 kcal/mol. This indicated a strong binding of the ligand with the trichothecene 3-O-acetyltransferase, preventing as a result the acetylation of the trichothecene mycotoxin and destruction of the “self-defense mechanism” of theFusariumsp.