Abstract: The diamondoid hydrocarbons in natural gas were detected by technique of heavy hydrocarbon concentration of natural gas and MID/GC/MS analysis.On basis of measured diamantane and vitrinite reflectance of source rocks in Qiongdongna basin,the relationship between diamantane index and vitrinite reflectance(R°)were established.Undoubtedly,it will show great significance for determining the maturity of the condensate and natural gas of Ying Qiong basin.