In order to obtain the influence law of environmental humidity on the self - healing performance of damaged ultra - high - performance concrete (UHPC), pre - cracks were induced in the specimens by loading, and then the specimens were subjected to secondary curing in four different environments: continuous immersion, wet - dry cycling, natural curing, and air - tight isolation. Subsequently, compressive and flexural tests as well as ultrasonic testing were conducted. The self - healing effects of UHPC were evaluated in terms of appearance characteristics, mechanical properties, density, and micro - morphology. The results show that environmental humidity has a significant impact on the self - healing performance of the specimens, the difference of self-healing rate under different humidity environments is due to the migration and transportation of water. In water - deficient environments (air - tight isolation and natural curing), no obvious healing products were observed at the cracks of the specimens, and the recovery rates of strength and density of the specimens were low. In water - saturated environments (wet - dry cycling and continuous immersion), the specimens had abundant visible healing products at the cracks, which were composed of calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C-S-H) gel and could effectively repair the cracks. The recovery rates of strength and density of the specimens were better in these environments. The recovery rates of strength and density of the specimens increased with the increase of the damage degree of the specimens. In the continuous immersion environment, compared with the specimens with a damage degree of 70%, the specimens with a damage degree of 90% had an increase of 16.59% in compressive strength recovery rate, an increase of 11.19% in flexural strength recovery rate, and a maximum increase of 64.43% in density recovery rate.