Cracks　within　concrete　accelerate　the　ingress　of　chloride　ions,　causing　acceleration　of　the　degradation　of　the　mechanical　performance　of　reinforced-concrete　(RC)　structures.　The　effects　of　cracks　should　therefore　be　considered　in　the　durability　design　of　RC　structures.　However,　the　available　test　observations　show　large　discrepancies　regarding　the　quantitative　effect　of　cracks　on　chloride　diffusivity　in　concrete,　and　the　corresponding　developed　empirical　formulas　have　some　limitations.　In　the　present　study,　a　unified　quantitative　relation　between　the　chloride　diffusion　coefficient　in　cracks　and　crack　width　was　developed.　The　parameters　in　the　proposed　formula　have　their　own　physical　meanings,　and　the　corresponding　curve　of　the　formula　is　smooth　without　an　inflection　point.　The　rationality　and　accuracy　of　the　developed　simplified　formula　were　verified　through　comparisons　with　test　data.　Furthermore,　chloride　diffusivity　in　cracked　concrete　was　studied　and　simulated　based　on　the　developed　simplified　formula,　and　the　effects　of　crack　width　and　crack　depth　were　examined.　The　simulation　results　indicate　that　chloride　diffusivity　in　cracked　concrete　is　significantly　affected　by　both　crack　width　and　crack　depth.　Moreover,　the　chloride　diffusion　behaviour　in　higher　strength　concrete　with　lower　porosity　is　much　more　sensitive　to　cracks　than　normal-and　lower　strength　concretes.