To quantitatively evaluate the effects of three different infiltration amounts on soil preferential flow, the morphological image processing technology, statistical sample variability analysis, variance analysis, and correlation analysis were used in this study. G20, G40, and G60 were taken to represent these plots with three different infiltration amounts (20 mm, 40 mm, and 60 mm respectively). Dyeing experiments with Brilliant Blue FCF (C.I. Food Blue 2) were conducted in grassland in Simian Mountain of Chongqing. The results showed that: (1) Dye coverage generally decreased with the increasing soil depth, and sharp decreases were found at the depths of 3 cm in G20 and 12 cm in G40, respectively. (2) The total dye coverage and length index of preferential flow were positively correlated with infiltration amounts (P＜0.01). (3) Water infiltration was promoted to deeper soil layers as the infiltration amounts increased, and the maximum depth of water infiltration reached 60 cm. (4) The non-uniformity of dyed coverage in preferential flow area and the maximum infiltration depth decreased with the increasing infiltration amounts with their variation coefficients ranging from 1.88 to 0.47, and 0.52 to 0.07, respectively. However, the effects of infiltration amounts on actual infiltration depth was even more complicated.