The 2008 M_w 7.9 Wenchuan earthquake triggered more than 56000 landslides and induced huge clastic sediment along the Longmen Shan orogen, which had impacted earth surface processes within the catchment. However, little is known about the changes in riverine sedimentary compositions and depositional processes associated with the earthquake. Characterized by high sedimentation rate (averaging 74 cm/a), the continuous sediment in the Zipingpu Reservoir, the lower reaches of the Minjiang River provides valuable records of sediment transfer and compositions before and after the earthquake. In this paper, the strontium isotopic ratio (⁸⁷Sr/⁸⁶Sr) and elemental concentrations of reservoir sediments were measured. The results showed that there are significant differences in both ⁸⁷Sr/⁸⁶Sr ratios and elemental compositions before and after the earthquake. Both ⁸⁷Sr/⁸⁶Sr and Rb/Sr ratios decreased after the earthquake, with a positive correlation with CIA, implying increased contribution of fresh debris to the river sediments by the earthquake-triggered landslides, in particular during 2010 and 2011 when there had intense monsoonal rainfall. The difference of sedimentary compositions before and after the earthquake provides a basis of potential tracers for reconstructing hydroclimatic and tectonic events and their environmental impacts using sedimentary records.