Plant health is determined by the comprehensive effect of soil physicochemical and biological properties. In this study, we compared the chemical properties and microbiomes of the rhizosphere soils of healthy, Fusarium oxysporum-infected, and dead watermelon plants and attempted to assess their potential roles in plant health and Fusarium wilt expression. The rhizosphere soils were collected from watermelon plants grown in a greenhouse under the same field management practices, and various soil microbial and chemical characteristics were analyzed. The rhizosphere soil of healthy plants had the lowest abundance of F. oxysporum and pH and the highest contents of ammonium (NH4+) and nitrate (NO3-). The relative content of hemicellulose was decreased in the rhizosphere soil of F. oxysporum-infected plants. The differences in soil microbial compositions among the watermelons at the three health statuses were obvious, and their microbiomes changed gradually along with plant health status. The microbiome in the rhizosphere soil of healthy plants had the highest relative abundances of potential antagonists and the lowest relative abundances of potential pathogens. The specific microbial composition together with some chemical properties of the rhizosphere soil of healthy plants might be responsible for inhibiting Fusarium wilt expression.