Abstract: To clarify the characteristics of substance transport and transformation in large reservoirs along the Lancang River, new equipment has been independently developed for automatic monitoring in the subsurface zone and intelligent sampling of water and sediment in a high and large reservoir. In-suit water samples with the maximum working water depth of 280 meters have been collected in 9 cascade reservoirs along the 1 290 km of Upper Langcang River in 2016, 2017, and 2018. In addition, multi-index monitoring at the water-sediment interface in reservoir riparian has also been conducted. It is found that cascade dams promoted the increase of the proportion of bioavailable phosphorus and ammonia nitrogen in water and the release of bioavailable phosphorus in sediments; The distribution of methylmercury in sediments was related to sediment particle sedimentation, regulated by hydraulic retention time and reservoir age. The emission flux of greenhouse gases increased due to the dam construction, while it was far lower than the world average level. The increase in frequency and area of wetting drying alternation in the subsurface flow zone strengthened the effect of nitrogen removal and thus reduced greenhouse gas release in reservoir riparian. The bacterial community could not be isolated by the dams. Water temperature was the key factor affecting the bacterial community on both the river scale and reservoir scale.