1999 was marked by tumultuous Sino-US relations. Riddled with unfathomable enigmas as well as extreme ups and downs, it should provide numerous clues for anticipation and bases for analysis of the forthcoming Sino-US relations in the twenty-first century. Through theory and analysis this article reaches the following preliminary conclusions: in the twenty-first century, the peaceful coexistence between China and US, with China already emerged into prominence, while the US still an international superpower, should be a main theme of the time, with US's China policy remaining to be one of strategic balance, exercising exchanges with precautions. China, in dealing with international relations, including those with the US, should free herself totally from the "shadow" of its past humiliations suffered under the aggression of Western powers. Correspondingly the US should shed its "attitude" based on Cold War and superpower mentality in dealing with Sino-US relations. Cooperation and competition shall be foremost the main theme in Sino-US relations. Normal exchanges between these two countries should be the best choice in developing Sino-US relations.