From that month freight trains will start running between Russia's Far East city of Khasan and the port at Rason, the North's northeastern free trade zone, the agency cited a top railway official as saying.
Work on repairing the 54-kilometre (32-mile) line began in October 2008.
It will connect to the Trans-Siberian Railway and help boost economic cooperation and relations between the two countries, the agency said.
The cross-border rail link is part of Russia's efforts to expand a foothold in the isolated nation. It is also building a cargo terminal in the Rason zone, formerly known as Rajin and Sonbong, which were two towns.
China has also been actively exploring investment opportunities in Rason and plans to build a separate cross-border rail link from Hunchun.
South Korea's Yonhap news agency reported in February that China had agreed to invest about $3 billion in developing Rason as an export base.
The impoverished North is striving to revitalise its economy through foreign investment in Rason, which was declared a special economic zone in 1991 but failed to flourish.