Liuxihe River, located in the transitional zone between the tropics and subtropics in southern China, is rich in macroinvertebrates that are characterized by species from both tropical and subtropical regions. Knowledge of the species richness and community structure provides useful information for rationalizing river ecological monitoring and assessment in this transitional zone. To explore species composition and the spatial distribution of macroinvertebrates and their relationships with environmental factors in the Liuxihe River, we sampled the macroinvertebrates and measured the environmental variables during the dry (March and December) and wet (June and September) seasons in 2018 at 20 upstream and downstream sites. We used multiple regression and multivariate ordination methods to analyze the relationships between environmental factors and macroinvertebrate communities. In total, we found 76 taxa (belonging to seven classes, 20 orders, and 50 families), among which the aquatic insects had the highest abundance, accounting for 69.39% of the total abundance. Chironomini was dominant with a relative abundance of 20.19%, followed by Corbicula fluminea, Semisulcospira sp. 1, and Caenis bicornis with relative abundances between 7% and 9%. The total abundance and species richness of macroinvertebrates negatively correlated with turbidity and total phosphorus during the dry season but positively correlated during the wet season. During the wet season, the macroinvertebrate communities in the three river classes significantly differed from each other, but not during the dry season. Canonical correspondence analysis (CCA) showed that water temperature, silicate, salinity, dissolved oxygen, turbidity, pH, and conductivity were the main environmental variables explaining the variation in the macroinvertebrate community in the Liuxihe River. However, habitat factors such as water depth and substrate character showed an unusual variation, which indicated that the river has been largely modified by human activity and further attention is required for ecosystem management in the watershed.