[Background] Chemotaxis of microorganisms mediated by root exudates is an important prerequisite for root colonization and function of plant growth-promoting rhizobacteria (PGPR), and further understanding of this process is of great significance to understand the colonization mechanism of the strains. [Objective] To study the signal substances in root exudates of potato which can promote the colonization of PGPR QHZ3 in rhizosphere. [Methods] The some phenolic acids in potato root exudates were identified by high performance liquid chromatography (HPLC). the chemotaxis of potato root exudates and different phenolic acids to isolate QHZ3 were compared using the semi-solid plate method and capillary-like method. the effects of different phenolic acids on biofilm formation of QHZ3 were observed by crystal violet staining. [Results] Phenolic acids in potato root exudates mainly included fumaric acid, p-hydroxybenzoic acid, ferulic acid and cinnamic acid. The semi-solid plate method shows that both the root exudates of potato and the four phenolic acids mentioned above had chemotactic effects on strain QHZ3, and the chemotactic effect of fumaric acid was the strongest. capillary-like quantitative test showed that the chemotactic effect of phenolic acids on strain QHZ3 was different at different concentrations. The chemotactic effect of middle and high concentrations of fumaric acid (25—100 μmol/L) and low concentration of ferulic acid (10 μmol/L) on strain QHZ3 was the strongest. Crystal violet staining showed that 120—240 μg/ml potato root exudates, 50—75 μmol/L fumaric acid and 100 μmol/L p-hydroxybenzoic acid could significantly promote biofilm formation of QHZ3, while ferulic acid and cinnamic acid had no significant effect on biofilm formation. [Conclusion] Both root exudates and phenolic acids could mediate the chemotaxis of strain QHZ3 to form biofilm in potato rhizosphere, but the effects of four phenolic acids were different. The chemotaxis of fumaric acid and ferulic acid was significant, while fumaric acid and p-hydroxybenzoic acid had significant effects on the formation of biofilm.