The coupled effects of external multi-ions and wet-dry cycles in sea water on the evolution of autogenous self-healing in cement paste were investigated. It was found that Mg2+, rather than Cl− and SO42−, in sea water plays a primary role in the healing process. The percentage of brucite in the reaction products of self-healing was more than 50%. The closure ratio of a 400-μm-wide crack after healing in sea water for 56 days was 2.6 times that of a crack healed in tap water. Furthermore, wet-dry cycles with wetting and drying periods that are each 12 h can significantly increase the healing efficiency by promoting the formation of brucite and calcite. Moreover, the promotional effect of external ions and wet-dry cycles on self-healing was more obvious in a crack with a larger width that facilitates the entrance of external ions during immersion and the evaporation of water in wet-dry cycles.