Inland-water dissolved organic matter (DOM) plays a key role in global and regional carbon cycling. However, DOM component and source characteristics in karst rivers have yet to be reported. Here we explored aquatic DOM during rainy season in a typical karst river-Furong River. Three-dimensional matrix fluorescence with parallel factor analysis (EEM-PARAFAC) was employed to reveal dominant components (C1, C2 and C3) of riverine DOM. Spatial variability and Spearman's correlation coefficients of optical parameters (SUVA₂₅₄, SUVA₂₈₀, E2:E3, S_290-350, BIX, FI, Frl, HIX, C1, C2 and C3) were analyzed. The results indicated that riverine DOC ranged between 1.08-3.89 mg/L. The DOC-normalized absorbance coefficients (SUVA₂₅₄ and SUVA₂₈₀) were lower than the other tributaries in the Yangtze River and varied between 1.89-6.63 and 1.64-5.14 L mg^-1 m^-1, respectively. This could be explained by the know "dilution effect" during rainy season. Riverine E2:E3 and S_290-350 served as proxies for DOM molecular size, which exhibited the similar tendency and were in the ranges of 0.85-3.25 and 0.002-0.012 nm^-1, respectively. Indeed, the concentrated rainfall triggered soil flushing of high molecular weight (terrigenous) DOM, and appropriate ambient temperature caused the rapid consumption of low molecular weight (endogenous) DOM, which collectively led to the existence of high molecular weight compounds but low E2:E3 and S_290-350 values. The PARAFAC deciphered 3 principal fluorescent components (i.e., humic-like, tryptophan-like and tyrosine-like DOM) in the Furong River, accounting for (35.3±13.8)%, (33.5±11.0)% and (31.2±21.7)% of the total F_max (%F_max), respectively. This was consistent with most tributaries of the Yangtze River, indicating that large contributions of biological processes were previously underestimated in karst rivers. Surface water BIX and Frl represented the recently produced DOM from autochthonous sources, which were high (0.91±0.07 for BIX and 0.75——0.94 for Frl) in the Furong River. Similarly, FI ranged from 2.14 to 2.39 and suggested a high potential in endogenous inputs. However, relatively low HIX values (0.54±0.16) underlined low humification in surface waters. Human activities greatly responded to DOM dynamics, and thus the highest F_max was observed in a densely populated town. Meanwhile, the F_max was also mediate by land use type, for instance, F_max values showed frequent fluctuations when rivers flowed through urban and farmland. Humic-like DOM (C1) abundance tightly linked to humification (HIX), while tryptophan-like DOM (C2) abundance was positively correlated with endogenous DOM production. This suggested that DOM components and origins exhibited the consistent variability. This study revealed the homogeneity of ecohydrological characteristics between DOM component, molecular size and origin in the karst river.