Carbon fiber reinforced polymer (CFRP) bars have excellent physical and mechanical properties and can be used to replace traditional prestressed steel bars. A model of prestressed concrete box girder with externally configured carbon fiber reinforcement was made, and experimental observations were conducted for 1001 days on the stress redistribution, long-term deflection deformation, and crack development of the box girder under continuous uniform load. Based on the measured creep coefficient of plain concrete columns, the bilinear method and curvature method were used to predict the long-term bending deformation of the test box beam. The experimental results show that the strain of compressive steel bars increases by 225% to 268% compared to the initial value, the strain of tensile steel bars increases by 36.2% to 38.6% compared to the initial value, and the compressive strain of concrete surface increases by 164% to 224% compared to the initial value. According to the current design specifications, the characteristic crack width under long-term load action is 11.8%~55.5% smaller than the measured value. The measured value of long-term bending deformation in the mid span is 2.32-2.42 times the initial deformation, which is 18.5% larger than the current design specifications