[Objective] A precise mesurement method for check dam carbon sinks at the small watershed scale was established and the vertical distribution patterns of soil organic carbon （SOC） in the dam land were elucidated to provide a scientific basis for carbon sink trading of check dams. [Methods] Taking the check dam system at Gaoxigou small watershed of Mizhi County， Shanxi Province as a case study， based on the 1：10 000 topographic map of 1978 and aerial survey data in 2024， the sediment deposition volume was calculated by fitting the dam height-area curve. A mechanical drilling rig was employed to conduct full-depth stratified sampling， obtaining 312 soil samples from five check dams in the study area for SOC content measurement. Combined with the sediment deposition data， the total carbon sink of Gaoxigou check dam system （including both erosion and emission reduction as well as vegetation and carbon sink increase） was calculated. [Results] The total sediment deposition of Gaoxigou check dam system was 1.39 × 10⁶ m³， with a carbon storage of 20 459.37 t （using carbon dioxide equivalent as the measurement unit）. The erosion and emission reduction was 7 160.78 t， and the vegetation and carbon sink increase was 489.75 t， resulting in a total carbon sink of 7 650.53 t. The vertical distribution of SOC in the dam land of Gaoxigou check dams exhibited a significant surface aggregation effect. However， an anomalous peak in SOC content was observed in the middle layer， potentially indicating the shaping effect of regional flood deposition history on the SOC vertical distribution patterns in the dam land. [Conclusion] The integration of aerial survey with early large-scale topographic maps can be directly applied to calculate the sediment deposition of check dam systems in small watersheds， providing important reference value for monitoring the carbon sink of check dams on the Loess Plateau.