Understanding the relationship between invasive plants and soil properties improves our ability to predict potential areas that could be invaded. To explore spatial scaling effects on the distribution of the invasive plant Alternanthera philoxeroides, we conducted field research at six rivers (three rivers were lightly invaded and the other three were heavily invaded by A. philoxeroides) near Nansi Lake, China, and compared characteristics of pairs of plots (4 m² in area) with and without A. philoxeroides on two scales. For each plot we measured plant-related parameters, including plant coverage; biomass; the carbon-to-nitrogen ratio in root, stem, and leaf; and soil-related parameters, including soil pH value, soil moisture, soil organic carbon (SOC), and soil total nitrogen (TN). At the river scale, rivers with higher SOC and soil TN had higher A. philoxeroides coverage. However, at the plot scale there was no significant difference in the soil properties of paired plots with and without A. philoxeroides. Only the root carbon-to-nitrogen ratio was correlated significantly with soil properties at the river scale, suggesting that roots played a vital role in the response to changeable soil conditions. Soil pH was negatively correlated with weed coverage, SOC, and soil TN. Invasive plant distribution may be positively related to SOC and soil TN of rivers, and efforts to prevent an A. philoxeroides invasion should focus on rivers with higher SOC and soil TN and lower soil pH.