In view that the indexes of the landform features and hydrological response of the study watershed have randomness, subjectivity, andmore correlation and less quantization between landform features and hydrological response, this paper obtained the lattice Boltzmann method solution of flow motion equation for river and slope, built a confluence model based on LBM, calculated the unit lines for the 25 study watersheds in the Heilongjiang River Basin, analyzed the relativity among the unit line elements, watershed area, watershed length and watershed width, and gave the quantitative formula. The results show that the time-area curve is more smooth than the distance-area curve due to the effect of the hydrodynamic diffusion.Unit time-area curve can be used to quantify unit line, but when the time-area curve of a watershed has many larger limiting values, there no good fitting of peak time difference and the flood peak. The finding can provide a method and a formula for quantitative watershed hydrological response and parameter calibration of watershed hydrological model.