Abstract: Three new structural tricyclic diterpenes are first reported in this paper. They are examined in the recent sediments of Qinghai Lake and their eluting time is between bicylic ter-panes of long chain and tetracyclic diterpanes of m/z 123 mass chromatogram. They are named as △^8.9-sandaracopimaradiene, dihydrorimuene, 13-isopimaradiene through the analysis of broken mechanism of fragments in mass spectrum and the contrast study of synthesized standard spectrum made by Weaver and Wenkert, their molecular ion peaks m/e are 272, 274,272.respectively,and correspond abundant peaks m/z are 257,259,137, respectively. The studied information about natural organic high molecular compounds shows that sandaracopimaric acid and pimaradiene acid had been isolated form resin acid and their structures had been identified. The authours deduce that sandaracopimaric acid and pimaradiene acid are the precursors of △^8.9-sandaracopimadariene, 13-isopimaradiene. In addition, many literatures have reported that sandara copimaradiane and pimaradiane have been detected in oil and source rock. Therefore,the three new structural tricyclic diterpenes studied in this paper are the middle transfer productuons form the acids in high plants to alkanes in geologic body, the eveolution process is that acid is transfered into alkene through dehydroxylation and then transfered into alkane through hydrogenation. The detection of △^8.9-sandaracopi-maradiene,dihydrori-muene,13-isopimaradiene not only enriched the types of biomarkers but also provided the proof for the transfer process of organic matter from organisms to geological body. These three new structural compounds examined in the recent sediment of Qinghai Lake reflects the information that organic matter in Qinghai Lake is not only derived from the organisms of the lake,but also has the input of terrigenous high plants.