Studies were conducted to ascertain the effect of biotic and abiotic environmental factors on the seasonal population fluctuation of H. armigera and relationships of its eggs and larvae on cotton variety (Giza 86) during four successive cotton seasons (from 2005 to 2008) that extended from the first week of April to the last week of September at Zefta district, in Gharbia Governorate, Egypt. Results showed that the H. armigera moths harboured to the cotton fields, as soon as, the cotton seedlings appeared. The moths have been existed in 4-5 main peaks with few minor peaks during the experimental seasons. The fruit cotton structures, (Receptors) began to emerge at the first half of May and continued to the end of the study period. Also, one to three main peaks of H. armigera eggs and larvae were existed per season. Statistically, multiple regression were judged by (full model) to predict the relationship between the dependent variables (eggs or larvae of ABW) that affected by four or five independent variables, lunar days, percentages of moon light, moths caught in light trap, eggs and cotton receptors, during 2005 to 2008 cotton seasons. The Analysis of Variance showed highly significant regression values between the expected eggs, larvae & trapped moths and lunar days, percent moonlight & the cotton receptors for the four experimental seasons. The expected eggs = (4.470) + (-0.121* lunar days) + (0.151*percent moonlight) + (1.023*moths) + (1.136*receptors). The expected larvae = (2.482) + (0.003*lunar days) + (-0.060*percent moonlight) + (-0.004*moths) + (0.342*eggs) + (-0.021*receptors) as average for the four seasons. The fit regression equation was represented with the r2 values which were 0.554 and 0.949 & the total effect 55.41 and % 94.9 and sum of the deviations square were 3339.21 and 44.57, respectively. Therefore, the previous four or five independent factors can be used to forecast population of ABW eggs or larvae before appearing of its peaks on cotton plants by enough periods to organize control measures and apply the recommended pesticides when really needed. Key words: Helicoverpa armigera (Hub.), American bollworm (ABW), Seasonal fluctuation & biotic and abiotic environmental factors.