Abstract: In order to explore the differences of water temperature variation in the natural-section and cascade reservoirs section of the Lancang River and the Nujiang River, the along-track rate of water temperature (RWT), reservoir renewal times (α number), water residence time and temperature continuation evaluation index are calculated by the field data at 32 monitoring sites from 2016-2020. The spatial distribution characteristics of water temperature were analyzed. The results indicate that: the longitudinal variation of water temperature in Nujiang River and Lancang River before the construction of the reservoir is relatively regular, which is basically consistent with the variation of air temperature along the river. The mean value of water temperature continuation evaluation index is only 0.04, indicating that the natural factors have limited influence on the spatial continuity of water temperature. Affected by meteorological conditions, the RWT of Nujiang River in different periods is slightly different, the maximum is 1.32℃·100  km-1 in January and the minimum is 1.02℃·100  km-1 in October. The average RWT of Nujiang River is higher than that of Lancang River in the natural state, which are (1.17±0.12℃·100  km-1)and（0.58±0.11℃·100  km-1）, respectively. The analysis suggests that the river flow may be the main factor causing the difference. Cascade reservoirs has significantly changed the natural variation characteristics of water temperature along the middle and upper reaches of the Lancang River. Affected by the lagged effect of water temperature in the reservoir, the water temperature has an obvious drop and fluctuates sharply along the river. The water temperature continuation evaluation index of Huangdeng Reservoir is significantly higher than that of other reservoirs, while the water temperature continuation evaluation index of Wunonglong, Lidi and Dahuaqiao reservoir is at a lower level, close to the state of natural rivers. The effect of cascade reservoirs on the spatial continuity of water temperature is complicated. Due to the combined operation of cascade reservoirs, the scale of single reservoir, and the regulation performance, the influence of different types of reservoirs is different.