Cyanobacteria blooms caused by water eutrophication are an urgent problem worldwide, and the frequency and scale of blooms with filamentous cyanobacteria are increasing continuously as the intensification of global warming. Plant secondary metabolite p-coumaric acid (p-CA) has biological properties such as scavenging free radicals, anti-inflammation, anti-tumor, and antibacterial, and have allelopathic effects on terrestrial plants, but its allelopathy on algae is less studied. In this study, the low concentration of p-CA (113 mg/L) can promote the growth of Limnothrix sp., while the high concentration (>127 mg/L) can significantly inhibit algae growth in a dose-dependent manner, reaching 99.55 % inhibition rate at the concentration of 153 mg/L. About 150 mg/L p-CA led to the destruction of algae cell structure, leakage of intracellular material, reduced photosynthetic pigments and protein content, inhibited photosynthesis, and stressed antioxidant system. Untargeted metabolomic analysis showed that 189 metabolites of Limnothrix sp. were significantly differentially expressed under the treatment of p-CA, and the metabolic pathways related to antioxidant stress and cell membranes were disrupted. In general, the above results indicate that p-CA is an effective allelochemical for inhibiting the growth of Limnothrix sp. and provide a new idea for the development of p-CA as a botanical agent for the control of cyanobacterial bloom.