Improving the outflow uniformity of long-culvert filling and emptying system for hydro-floating ship lift can reduce the ship chamber’s inclination，thus it is the basis of safe operation of hydro-floating ship lift. Through theoretical derivation，main influential factors of outflow uniformity are determined. Based on the two dimensional mathematical model，we simulate the outflow process during ship-lift’s operation，define the standard deviation of branch flux in particular moment as the characteristic index to measure the outflow’s uniformity. The response mechanism between outflow uniformity and related factors is derived and sensitivity analysis is conducted.