A large number of the collapse, landslides and debris flows at different scales triggered by Wenchuan Earthquake are great sources of sediment for the river in earthquake area. To study effects of earthquake erosion on sediment transportation after Wenchuan Earthquake, field investigation and measurements were performed for the landslides and avalanches on the Mianyuan River. Based on the data for the past 5 years, 1.15×10⁸ m³ deposits were produced during this earthquake equivalent to about 100 times of the amount of soil erosion for a normal year, most of which were deposited and accumulated in the tributary ditches or channels. It indicated that only a few part of fine sediments were transported to the downstream as suspended load, as the dominant coarse particles were over the transportation capacity of the rivers without distinct change of hydrological conditions during the last five years. Although earthquake erosion resulted in a huge amount of sediment in the upstream Mianyuan River, the annual sediment discharge had no obvious difference from that before the earthquake, which showed that the effects of sediment from earthquake erosion on sediment transportation in the lower Mianyuan and Tuojiang Rivers are limited in the short term.