The global transition from undisturbed to human-dominated landscapes has impacted river water quality worldwide and made the quantification of land use a valuable indicator of water pollutant. The Ganjiang River, as the largest tributary of the Poyang Lake Basin, is the main pollution source of the Poyang Lake. Identifying the influence of land use on water quality in the Ganjiang River has great significance for water environment protection in the Poyang Lake. In this study, we investigated the monthly concentration of NH₄⁺-N, TP, COD_Mn and DO in seven major tributaries of the Ganjiang River in 2012 and analyzed the influence of land use on river water quality by the methods of correlation analysis and redundancy analysis. Two spatial scales, the sub-basin and buffer zone, and two levels of land use classification were considered. The first level of land use classification was paddy field, dry farm, forest land, grass land, water area, resident construction land and unused land, resulting from remote sensing image interpretation. The second level of land use classification was obtained from the first level based on different geomorphology, canopy density, grass coverage and other factors. The results showed that forest was the largest land use pattern in the study area, followed by paddy field and dry farm. The concentration of TP had a significant positive correlation with NH₄⁺-N in wet season, while NH₄⁺-N had a significant negative correlation with DO in dry season. The pollution sources of TP both in wet season and dry season were from hill paddy field, urban land, reservoir and pond. The pollution sources of COD_Mn were from paddy field, urban land, reservoir and pond, and rural residential land in wet season, while from plain paddy field and rural residential land in dry season. The pollution sources of NH₄⁺-N were from urban land, reservoir and pond in wet season, while from urban land, mountainous dry farm, riparian forest land and low coverage grassland in dry season. Additionally, different spatial scales of land use had different impacts on water quality indicators. The land use in sub-basin had more influence on TP and wet seasonal COD_Mn than that in buffer zone, while it had less influence on dry seasonal COD_Mn than that in buffer zone. For NH₄⁺-N, the land use in sub-basin had similar influence as that in buffer zone in wet season, while less influence than that in buffer zone in dry season. The impact of land use on DO was not significant. Moreover, we found that it was more helpful to study the source of the river water pollutant based on the second level of land use classification than the first level of land use classification. Among the paddy field, hill paddy field was the main source of TP and wet seasonal NH₄⁺-N; while plain paddy field was the main source of dry seasonal COD_Mn. Among the residential construction land, urban land was the main source of TP, NH₄⁺-N, and wet seasonal COD_Mn, while rural residential land was the main source of COD_Mn. Among the water area, reservoir and pond were the main source of TP, wet seasonal NH₄⁺-N and wet seasonal COD_Mn.