Reconstruction of original total organic carbon (TOC) in source rocks is the key and difficult point of hydrocarbon source rock evaluation. The paper focuses on the sediments of Buha River estuary in the northwest of Lake Qinghai, and a new method of original TOC reconstruction via born element in sediments was discussed. The sediments of Buha River estuary sediments are mainly made of mud, silt, fine sand and transitional type composition. The sediments are generally have low clay mineral content. The main types of kerogen in the sediments were Ⅱ₁ and Ⅱ₂, and most of organic matter come from terrigenous organisms while a small quantity of organic matter come from aquatic organisms. TOC in Buha River estuary sediments is in the range of 0.02% to 4.29%. TOC in the sediments of semi-deep lake and prodelta is usually higher than that in other environmental sediments. Organic matter has a significant effect on the enrichment of some trace elements. There is a significant positive correlation between the trace element concentration and TOC content in the sediments, the trace elements include boron, cobalt, nickel, zinc, gallium, rubidium, cesium, lead and uranium. The enrichment ability and intensity of organic matter to trace elements are controlled by the contact time of sediment and water, and so the correlation between trace element and TOC has obvious difference in different sedimentary environment. TOC is higher in sediments of fluvial, delta plain, prodelta, shallow lake and semi-deep lake environment, while it is lower in sediments of lakeshore environment. Boron was the most sensitive to the variation of organic carbon content, and the content of boron in the sediments of intermittent exposure environment like lakeshore is also showed a significant positive correlation with TOC. Boron is an effective index that can reflect original organic carbon content of the hydrocarbon source rocks. According to the excellent linear relationship between the boron concentration and TOC in the sediments of Buha River estuary, a formula for the quantitative calculation of the original organic carbon content via the content of boron in the source rock was established. The formula is suitable for the reconstruction of the original total organic carbon in the terrestrial brackish water and salt water of environment.