This thesis tries to find the reason why China and Russian haven't form an alliance to balance the United States as it has been the sole superpower of the world since the end of the Cold War. This question is always discussed among IR students because the absence of balancing behaviors to counterbalance the United States is an important topic for scholars and theorists for a long time. And among all the second-tier countries, Russia and China are always regarded as the most competitive ones considering about the history and the reality of their comprehensive national power. Inspired by balance of power theory and its modifying theories, the thesis organized three hypotheses from three aspects: the incentive of building the Sino-Russian alliance, the opportunity of building a Sino-Russian alliance, and the alternatives of a Sino-Russian alliance. After being tested, the second and the third hypotheses are proved to be reasonable while the first one is not. China and Russia have enough incentive to balance the United States; they haven't build an alliance because their domestic conditions reduced the opportunity and they can adopt soft balancing strategy to balance the United States so that they don't have to build a formal alliance right now. Key Words: Sino-Russian Relationship Alliance Balance of Power