In Ethiopia, dams are adversely severed by sedimentation due to soil erosion from the watershed area. This specific study was conducted on Abrajit reservoir in east Gojjam, Amhara region, Ethiopia. The general objective of this study was to investigate reservoir sedimentation and estimation of watershed sediment yield to reservoir. Bathymetric survey using eco-sounding (Garmin GPSMAP421s) was conducted and topo map of reservoir data were used for estimation of the sediment volume. For estimating sediment volume from bathymetric survey and top map data, ArcGIS 10.5 version and Golden surfer 16 latest version was used. The triangular interconnected network (TIN) map was developed for both the initial and measured elevation data using ArcGIS. The deposited sediment volume was estimated by subtracting the TIN map of initial bed level from the Tin map of measured bed level. For estimation of annual sediment load contributed from the watershed RUSLE model was conducted. The result of the study revealed that to date, 343,700m3 volume of sediment was accumulated in the reservoir that reduces 20% of the total reservoir capacity. From the sediment model, annually a total of 28,641.68 m3 sediment is coming from the watershed to reservoir that contributed 1.66% of annual reservoir volume reduction. From comparison of remining reservoir storage and annual sediment load, the reservoir will not serve more than 12 years. The measured current storage capacity for Abrajit dam was 1,388,870m3. The estimated sediment delivery ratio (SDR) for Abrajit reservoir and its watershed was found to be 96 %. The estimated specific sediment yield (SSY) was found to be 4733.387 tonkm-2y-1. The mean annual soil loss generated from the entire watershed was 40.6 ton/ha. Reservoir capacities running to reduce as a result, operation curves should be mandatory to give water service for the critical water needs and Regular monitoring of sediment deposition in reservoir is recommended. Therefore, to improve the estimated life span of reservoir watershed management is very important and further study is need to identify area where watershed development will focus to the future.