Habitats with different numbers of plant species (S) may exhibit varying levels of invasibility when invaded by invasive plants (IPS). Nevertheless, there are still doubts about the relationship between S and IPS’ invasion intensity as well as the community invasibility. It is also unclear which environmental factor has the greatest influence on the community invasibility, especially in habitats with different S. A cross-plot comparison approach was employed to estimate the differences in IPS’ relative abundance and invasion intensity, the community invasibility, and plant taxonomic diversity along a gradient of S under the invasion of Erigeron annuus (L.) Pers. Plant diversity, dominance, evenness, and richness evidently increased with increasing S. The relative abundance and invasion intensity of E. annuus, as also the mean, maximum, and minimum relative abundances of all plants, and the community invasibility significantly decreased with increasing S. The community invasibility was positively regulated by the relative abundance and invasion intensity of E. annuus, but negatively regulated by plant diversity, dominance, evenness, and richness. Therefore, protecting the diversity of native plants is crucial for enhancing the resistance to IPS’ invasion.