Abstract: To study the mass transport process in an estuary, residence time and exposure time were calculated for five boxes in Daliaohe Estuary in three typical runoff conditions using a three-dimensional convection-diffusion model based on Finite-Volume Coastal Ocean Model (FVCOM). Data were obtained for both the time required to leave the control domain for the first time and the total time spent in the control domain. Then, the return coefficient and the subdomain exposure time matrix which show the interaction between boxes were also investigated. The results showed the interaction between the runoff and tides control the residence time in Daliaohe Estuary. Exposure time and residence time have the same change trendency, but they differ greatly in size. Exposure times are 8, 3 and 1 days more than residence times during dry, normal and rainy seasons, respectively. The return coefficient could reach 0.94 at the downstream end during dry season, with the tracer returning to this area many times. The downstream boxes have little influence on the upstream boxes in Daliaohe estuary except for the case in the downstream end at the maximum flood tide.