Phytoremediation of heavy metal–contaminated sites has been widely used. Nonetheless, the destruction of chloroplasts and plant growth enzymes by heavy metals leads to a low germination rate and high mortality of plants. To address these issues, an experiment was conducted in which plants were grown with (SHC) and without humic acid (SC) in actual Cd-contaminated soil from the site of an industrial pollution source. The results showed that the average germination rates of SC and SHC samples were 94.17% and 98.33%, respectively, and the plant heights were approximately 5 and 7 cm after 42 days of planting, respectively. It was discovered that humic acid (HA) enhanced plant growth by increasing urease and invertase content of the soil. The Shannon index and Venn diagram revealed that SHC had the richer population diversity. High-throughput analysis demonstrated that HA increased the content of plant growth-promoting bacteria in the soil from 5.01 to 34.27%. The experimental results revealed that HA increased microbial activity and diversity, thereby providing a favorable environment for plants to thrive. This study develops an effective method to enhance the phytoremediation performance of heavy metal–contaminated soils.