In the process of flexible mattress sinking in waterway improvement engineering，the precise control of mattress location is an important factor that affects the success and quality of construction. Currently，the selection of sinking parameters mostly depends on empirical judgment because of the lack of theoretical and experimental research. Through the generalized flume experiment，the influence of different parameters on drift distance of mattress head in the process of downstream sinking was studied，and the sensitivity difference of each parameter was quantified. Based on the theory of multivariate nonlinear regression，a prediction model of the drift distance of mattress head under the effect of multiple factors was established，and its prediction accuracy was statistically analyzed by using correlation coefficient，mean absolute percentage error，etc. The experimental results show that the drift distance decreases with the increase of beam weight and rope length，while increases with the increase of water depth and velocity. The sensitivity order of each parameter from largest to smallest is velocity，relative rope length，water depth and beam weight. The study results can provide a scientific basis for the construction of flexible mattress sinking.