Composition and species diversity of catches caught by pelagic longline fishing in the tropical Western and Central Pacific Ocean (WCPO, 2°03′─11°17′S 163°14′─173°35′E) during May 2018 and Mar 2019 were analyzed. The generalized linear mixed model (GLMM) and circle statistics methods were used to assess the effects of temporal and spatial factors, such as water depth and lunar phase, on the catch composition and species diversity. The results showed that: (1) the total number of catches was 3673, and catches consist of 35 species, in 30 genera, 21 families, and 9 orders. According to index of relative importance (IRI), bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacores) are dominant species, while blue marlin (Makaira nigricans), albacore (Thunnus alalunga), silky shark (Carcharhinus falciformis), long-snouted lancetfish (Alepisaurus ferox), and pelagic stingray (Pteroplatytrygon violacea) are important species. (2) The CPUEs of bigeye tuna, yellowfin tuna, and bycatch species were (1.66±0.89), (1.39±1.45), and (2.52±1.27) ind/1000 hooks, respectively. The ShannonWiener (H'), Margalef (D) and Pielou (J) indices were (1.78±0.28), (2.53±0.60), and (0.79±0.09), respectively. (3) The GLMM model fit indicated that the lunar phase (cosine) had an extremely significant effect on the CPUE of bigeye tuna (P=0.001, higher CPUE in full moon and lower in new moon), and the lunar phase (sine) had a marginal effect on the CPUE of yellowfin tuna (higher CPUE in the first quarter and lower in the last quarter lunar phase). As for bycatch species, no significant effect of lunar phase on CPUE was detected. Water depth had a highly significant effect on CPUEs (P＜0.001). (4) No significant effect of lunar phase on species diversity indices was detected. However, water depth significantly influences the Shannon-Weiner index (H′) and Margalef index (D) (P＜0.001). The results revealed that the high richness of species and complexity of community in the tropical WCPO would provide good community tolerance to environmental changes and fishing activities.