Abstract: The main reason for the decrease of sediment transport in the lower reaches of the Jinsha River is reservoir trapping, which has a great influence on the condition of the inflow and sediment of the Three Gorges Reservoir. To develop a complete understanding of the situation of reservoir trapping in the Jinsha River basin, based on the reservoir construction and the hydrology and sediment data collected in the basin since 1956, with the method of empirical formulas and by using typical investigations and the principle of sediment transport balance, the sediment storage capacity in the middle and lower reaches of the Jinsha River in the recent 60 years and the contribution weight of reservoir trapping to sediment reduction in the Jinsha River basin were studied quantitatively. The results indicated that the contribution weight of reservoir trapping to the sediment reduction at Pingshan station from 1956 to 1990, 1991 to 2005, and 2006 to 2015 was 0.3%, 48%, and 83%, respectively. It is apparent that the effect of reservoir trapping increased gradually. From 1956 to 2015, the annual sediment trapping in the reservoirs of the Jinsha River basin was 0.310×10⁸ tons, and 89% of this sediment was silted in the large reservoir. Especially, from 2011, with the completion of the reservoirs in the middle and lower reaches of the Jinsha River and the Yalong River, the annual reservoir trapping in the Jinsha River basin increased to 1.92×10⁸ tons, the contribution weight to the annual sediment reduction at Pingshan station was more than 90%.