The invention discloses a dispersion test method applicable to low-permeability soil. The method comprises the steps as follows: a permeameter cavity with flexible side walls is filled with a test earth pillar; the permeameter cavity is arranged in a hydraulic pressure chamber; two ends of the permeameter cavity are connected with a tracer agent injection assembly and a tracer agent collection and detection assembly respectively; the hydraulic pressure chamber is connected with a pressurization assembly for pressurizing water injected into the hydraulic pressure chamber; the dispersion parameter of the test earth pillar is detected by the tracer agent injection assembly and the tracer agent collection and detection assembly while the hydraulic pressure in the hydraulic pressure chamber is kept. The dispersion test method has the advantages that under the action of the hydraulic pressure in the hydraulic pressure chamber, the test earth pillar is closely wrapped with the flexible side walls, and side wall permeation caused by gaps between the test earth pillar and the flexible side walls is avoided; meanwhile, the test earth pillar is kept compact and not prone to breakage under the hydraulic pressure.