High-performance concrete (HPC) is crack sensitive. The emergence of cracks reduces the durability of concrete. In the marine environment, HPC tubular piles act on the foundation with water pressure and are more susceptible to chloride ion erosion. This paper studies the impact of the cracking performance and the cracks of different depths and widths of HPC with fly ash on chloride ion permeability. The experimental results show that the pozzolanic activity and filling effect of fly ash enable the HPC to have higher crack resistance grade. The penetration depth value of chloride ions increases with the crack width and depth. Compared with the crack width, the crack depth has a more significant effect on chloride ion permeability. The research in this paper provides the experimental foundation for the chloride ion erosion of offshore HPC tubular piles.