[en] The reactor pressure vessel (RPV) suffers from serious pressurized thermal shock (PTS) which is caused by the cold safety injection fluid direct into RPV downcomer in AP1000. In this paper, the Transient States of Temperature of RPV direct vessel injection nozzle(DVI-Nozzle) in AP1000 under the different operating conditions has been investigated using computational fluid dynamics (CFD) code ANSYS-CFX. Results show that the DVI-Nozzle experiences a large step change in temperature in each operating condition which causes the strong effect on the safety of RPV. (authors)