Abstract: By using high temperature GC analysis of high wax oil and rock extracts in Damintun Depression,the distribution and composition of high molecular weight hydrocarbons (HMWH_s) were determined.Except for high molecular weight n-alkane,complete isoparaffin or cycloparaffinic hydrocarbons were observed in hydrocarbon of C₄₀ above.Their abundance and distribution are controlled by thermal evolution of source rocks.It proved direct evidence of origin of high wax oil as a result of detection of HMWH_s.