Based on the data of systematic survey in the field and observation in the laboratory, the natural population life tables of continuous two generations of the diamondback moth (DBM) , Plutella xylostella L., were constructed on one cropping of flowering Chinese cabbage in Shenzheng, Guandong Province. The results showed that the indices of population trend of two continuous generations of DBM were 11. 9 and 24. 4, respectively in spring and autumn. Parasitoids played a determinant role in the control of natural population of DBM. In spring, the important factor influencing the natural population of DBM was the larval-pupae parasitoid, Oomyzus sokolowsakii (Kurdjumov), which exclusive index of population control (EIPC) reached 8. 28. While the EIPC of Cotesia plutellae Kurdjumov was 4. 85. In autumn, C. plutellae was the secondly important factor influencing the natural population of DBM, which EIPC was 3. 67. The low EIPC (1 .2) of O. sokolowsakii caused a high population increase of DBM in autumn.