Abstract: By using only 10 descriptors which was screened out from large amount of arbitrary terms based upon the quantitative pattern re-cognition(QPR) program designed in this laboratary1,the structure-carcinogenic activity relationship(SCAR) of 153 N-nitroso com-pounds(NNC) with excellent agreement of 97.3% between calculations and animal tests, has been established in this work. In light of these 10 descriptors with definite biologic contents and the experimental facts of SCAR, it must come to the conclusion that the major trend of carcinogenic activation of NNC, is the crosslinking of DNA complementary base pair through the bifuntional alkylation between the α-position and the β-position carbonium ions or transition species, if the γ-position just corresponds to a ω-position, the carbonium ion on γ-position will play important contribution also to the bifunctional activation. The distance between both active centers approaches to 2.80-3.00Å and is just matching with the two negative centers in DNA complementary base pair along the double helix. Therefore, the comprehensive metabolic process of NNC for carcinogenic activation and metabolic detoxication by the catalysis of monooxygenase may be generalized to a schema as follows.