This paper analyzes the motives and evolution of the construction of the Russia-Belarus Union, introduces the assessments of the west, Russia and Belarus towards the Russia-Belarus Union and its prospects, with a focus on the problems and difficulties during the process of Russia-Belarus Union company. The author thinks the Russia-Belarus Union is based on their geopolitical strategic interests. There is still a long way for the integration of Russia and Belarus. However, no matter what political changes occur, both Russia and Belarus will spare no efforts promoting the cooperation between these two nations.