Abstract: China's flight delays have been getting worse in recent years, so more attention should be paid by civil aviation industry and the public. In order to improve the situation, the first step is to find the real root cause of flight delays. The reasons of flight delays that are recognized by the industry management department and experts are not the fundamental cause, so it cannot find out effective measures to deal with the flight delays. The primary cause of flight delays is the contradiction between the rapid growth of the aviation transportation and the limited use of airspace resources, and the other three contradictions. Therefore, we should aim at the four major contradictions and find a way to solve the contradictions, and step by step, flight delays can be improved.