Abstract: In coastal area roadbed projects, capillary water rise can produce roadbed diseases and affect the safety and durability of road operation, so it is especially important to study the capillary water rise height. The article regards capillary water rise as a kind of unsaturated soil seepage phenomenon, introduces fractal dimension to unsaturated soil permeability coefficient correction, and then proposes a capillary water rise height model based on fractal theory, and obtains the capillary water rise height curve with time; and then conducts a vertical tube method capillary water rise height test on a mainline roadbed soil sample in Nantong, changes the dry density of the soil sample and the fractal dimension of the initial particle size distribution to do control group test. The results of the study show that: the capillary water rise showed a rapid increase at the beginning, and then slowly increased, and finally stabilized trend; the larger the fractal dimension of the particle size distribution of the soil sample, the greater the capillary water rise height; the smaller the dry density of the soil sample, that is, the greater the porosity, the greater the capillary water rise height. In the capillary water rise height model proposed in the article, the capillary water rise height is related to the sample porosity, saturated permeability coefficient, capillary water rise height corresponding to the inlet value, fractal dimension, etc. In the calculation of the theoretical value of the model, it is considered that the fractal dimension change only changes the capillary water height corresponding to the inlet value, not the saturated permeability coefficient, while the dry density change, i.e., the porosity change only leads to the saturated permeability coefficient change, does not change the Intake value corresponding to the height of capillary water, the obtained model calculation results are consistent with the trend of the test results, verifying the correctness of the theoretical model, providing theoretical guidance for the prevention and control of road base capillary water disease.