Abstract: Based on the data of the light falling net survey from August 23 to September 26, 2018, the species composition and diversity characteristics of pelagic nekton of the Northwest Pacific Ocean were analyzed, using the relative importance index, species richness index, Shannon-Wiener index, and Pielou index.The results indicated that 45 nekton species belonging to 9 orders, 21 families and 37 genera were identified in this survey.Among them, Chondrichthyes included 2 orders, 2 families, 2 genera and 2 species;Radiopods included 6 orders, 17 families, 31 genera and 39 species;and Cephalopods included 1 order, 2 families, 4 genera and 4 species.The mean biomass and catch number of nekton in the investigating area was 1 126.64 kg/h and 41 727.11 ind/h, respectively.Scomber japonicus and Sardinops melanostictus were the absolute dominant fish, with the relative importance index of 3 154.11 and 2 525.95, respectively.This may be related to the fact that the production area was historically an important feeding area for important pelagic fish such as S.japonicus and S.melanostictus.The average Shannon-Wiener index(H') was 0.70, and the range was from 0.00 to 1.74.Species richness index(D) was 0.36, and the range was 0.00~1.08.Pielou index(J') was 0.48, and the range was 0.00~0.97.The dominant species in this area were obvious, but the species composition was relatively simple and the diversity level was low, which might be due to the small species composition, low interspecific competition and low degree of niche crowding among the oceanic areas.The diversity index showed a trend of higher in the south and lower in the north.The northern part of the surveyed area was a fishing ground for economic species, so the diversity level was low.