Invasive species have competitive advantages over neighboring native species and decrease the biodiversity of the local community. The novel weapon hypothesis suggests that invasive plants affect local plants and suppress soil-borne pathogens by exuding allelochemicals to facilitate invasion. Therefore, the following study was designed by focusing on the extracts derived from certain parts of plants, and the impact of the collected root exudates of invasive plants on soil-borne pathogens has been documented, but there is still a need to identify its mechanisms. We conducted several experiments to test whether the alien invasive plant species Wedelia trilobata (L.) Hitchc. can suppress soil-borne pathogens through its root exudates. We also attempted to explain the inhibition mechanism of the root exudates on soil-borne pathogens. The results showed that the root exudates of W. trilobata significantly inhibited the growth and activities of soil-borne pathogens under sterile petri dish and sand cultures. Specifically, root exudates decreased the conidial germination, mycotoxin production, and hydrolytic enzyme (pectinase, cellulase, and amylase) activities of soil-borne pathogens in liquid culture, indicating the inhibition mechanism of root exudates of W. trilobata on soil-borne pathogens. Our results provided direct evidence that the root exudates of W. trilobata help it to spread by suppressing resident pathogens and promoting its invasion.