Aiming at the problem that the main tower of Yangmeizhou Bridge may crack due to the difference in the age of old and new concrete. In this paper, a study for crack resistance of interface between the old and new concrete was proposed. Firstly, through the comparison of the crack resistance of the new and old concrete structures under the conditions of different concrete mix ratios, different fiber lengths and content, and different treatment methods of the new and old concrete joint surfaces, a treatment plan for the joint surface of new and old concrete with better crack resistance was proposed; Secondly, the shrinkage stress of the interface between the new and old concrete through Midas Civil software. The results show that under the same fiber content, the anti-shrinkage effect of long fiber concrete is better than that of short fiber concrete; Compared with the benchmark concrete, the shrinkage rate of the long-fiber polypropylene concrete mixed with 0.92kg/m3 is the smallest, and the shrinkage rate is reduced by 269×10-6; Incorporating long fibers can significantly reduce the crack width, but the number of fine cracks has increased. The best way to treat the bonding surface is to chisel the surface of the old concrete and paint the interface agent, and then pour the fiber concrete, the bonding performance is higher than other treatment methods. Numerical analysis results show that under the optimal treatment plan, the maximum bond tensile stress of the interface between the new and old concrete has been reduced from 3.10MPa to 2.45MPa, which effectively reduces the shrinkage stress of the interface between the new and old concrete.