Abstract: The water injected through the direct vessel injection（DVI） nozzle is easily bypassed out to the broken cold leg by a cross flow of high-speed steam in the downcomer during a large-break loss-of-coolant accident（LB-LOCA） for the reactor using DVI technology. This bypass fraction of the injected water due to the cross flow could reduce the water into the reactor core,which is considered to be an important safety issue. A numerical model during the LB-LOCA reflood phase is developed to investigate the steam-liquid two-phase flow behavior for a typical pressurized water reactor. The bypass fraction and the water level in the downcomer with the time are obtained for evaluating the cross flow effects by computational fluid dynamics（CFD） analysis.It is found that the present study could model the key physical phenomena reported in other experimental study. The results indicated that this analysis practice could be guidance for the DVI design and improve our understanding of the reactor thermal-hydraulic behavior.