In order to evaluate the repairing effect of prestress reinforcement of the aging deteriorated concrete， studies of the flexural capacity in the negative bending moment zone of continuous composite beams with prestressed reinforcement are carried out. The static load tests of four prestressed composite beams under concentrated load are finished. The impacts of different shear connection degrees upon the mechanical performance of the prestressed composite beams are discussed, and the load midspan deflection characteristics of the beams are analyzed. The formulae for calculating elasticity and ultimate bearing capacity in the negative bending moment zone are established. The analysis results show that the flexural rigidity and the bearing capacity of full shear connection beams are greater than those of the partial shear connection beams, while the flexural rigidity and the bearing capacity are not in direct proportion to the shear connection degree. The comparison between the calculated and measured bearing capacity is made, and both errors are within 10%, so the results given by the new formulae can satisfy the engineering accuracy requirements. The calculation formulae derived for the flexural bearing capacity of the negative bending moment zone of the prestressed composite beam have some calculation accuracy in this paper, which is for design reference only. Since the calculated value of the ultimate flexural bearing capacity is less than the measured value, the calculated results given by this study are safer for the project design.