Based on the vertical static test of two prestressed steel reinforced concrete frames，their characters, including failure pattern, crack development, rigidity change and moment redistribution, were investigated.The test results have shown that prestressed steel reinforced concrete frame beams,similar to under-reinforced concrete beams, are ductile failure; plastic hinges appear and plastic redistribution of internal forces is achieved on the frame beam end; and the ductility ratio of displacement is greater than 3. Moment redistribution values are about 30%, which is higher than ordinary prestressed concrete structures. The generation nature of secondary forces was analyzed and the calculation formula of ultimate flexural load-carrying capacity, crack resistance, stiffness and maximum crack width were presented, which consider secondary internal forces, including secondary moment and secondary axial force. The calculation results agree well with the test values. The calculation theory in this paper reflects new ideas of modern prestressed design and can provide reference for the establishment of “Prestressed Concrete Structure Design Code”.