As a fundamental of the navigation simulation to understand the passage possibility through the Northern Sea Route (NSR), the navigation simulation is performed during the sea ice decrease period (2007 to 2011) with the sea ice concentration reanalysis. Under even the strictest sea ice condition, the continuous passage period through the NSR is roughly from the end of August to the beginning of September of each year during 2009 to 2011. The period through the NSR in each year is not fixed. The simulation in this study will evaluate whether ships can pass through the NSR and whether escort ships are needed.