The capillary rise is capable of revealing the mechanism involved in groundwater evaporation. Among the parameters of this experiment, the maximum rate of groundwater evaporation （Emax) is an indispensable parameter in the calculation of groundwater evaporation, which can be estimated by the Gardner model. When using the Gardner model, it has widely been accepted to ignore parameter b during hydraulic conductivity prediction for simplification purpose, which may yet affect the prediction accuracy. Therefore, an investigation on how b affects Emax is necessary. Loam soil samples from Yangling, Changwu, and Linyi regions were selected for indoor capillary rise and one-dimensional evaporation experiments, with two solutes (KCl and NaCl) that were dissolved in groundwater at three concentrations (1, 5, and 30 g/L) and one control treatment (CK) of distilled water without any salt solutions. Then Emax was calculated by the observation of the capillary rise and the sensitivity of b in the Gardner model was evaluated. Results indicated that the capillary rise rate of the treatments supplied by salty groundwater was larger than that supplied by distilled water, which further led to a larger Emax; besides, the capillary rise rate and Emax decreased with the increase of the salt concentration when the concentration of KCl and NaCl solutes was in the range of 1-30 g/L. Furthermore, during the prediction of the Gardner-model-based Emax, ignoring b and considering b always caused an overestimation and underestimation, respectively. And the Gardner model considering b had higher accuracy for Emax prediction, with the relative error of 1.16%-4.50%. Moreover, the influence of ignoring b on Emax gradually weakened with the increase of the b value. Improving the accuracy of Emax prediction can benefit the decision-making of cropland irrigation schemes and the understanding of groundwater evaporation mechanism.