Abstract: Based on the field investigation of farmland ecosystem in Songyang County, Zhejiang Province, the species composition, altitude distribution pattern and habitat preference of invasive weeds were studied. The results showed that a total of 10 species of invasive weeds were recorded, belonging to 7 families, with Compositae plants being the most represented family (4 species), accounting for 40.0% of the total species. The invasion intensity (average coverage) exhibited a declining trend with the increase of altitude. The average coverage in the low-altitude group (＜150 m) was 64.5%±22.0% (n=9), which was higher than that in the mid-altitude group (150–250 m, 48.0%±15.2%, n=8) and that in the high-altitude group (＞250 m, 34.7%±9.0%, n=3), with the Kruskal-Wallis test showing the marginal significance (H=5.95, P=0.051). The Chi-square test showed that the distribution of species was significantly correlated with altitude (χ²=34.49, P=0.011). Ageratum conyzoides was exclusively distributed in the high-altitude areas, while Pontederia crassipes Mart. was concentrated in the mid-altitude areas. The results provided a reference for monitoring, early warning and classified prevention and control of invasive weeds in the mountainous regions of southern Zhejiang.