Prestressed concrete girder bridge is popular in engineering field for its advantages of good structural stiffness, smooth running and simple maintenance. However, in recent years, in the construction process or use stage of long-span prestressed concrete beam Bridges, there are generally a variety of diseases of different nature, the most common diseases are box girder cracking and long-term structural deflection; These diseases pose a threat to the durability and operation safety of Bridges, and even hinder and restrict the development of long-span prestressed concrete girder Bridges to a certain extent. In view of the diseases of existing long-span prestressed concrete beam Bridges, the causes of the diseases, the diagnosis of bridge damage, the repair and strengthening methods of damaged Bridges are urgent problems to be solved in the application of such Bridges. In this paper, the diseases of existing long-span beam Bridges in China are described. The causes of these diseases of long-span prestressed concrete beam Bridges involve design calculation, construction technology, maintenance management, material properties, etc. The causes of each typical disease are analyzed, and corresponding preventive measures are given, in order to benefit the actual project.