Chub mackerel (Scomber japonicus) is one of the important fishery resources in the northwest Pacific Ocean. Building a scientific forecast model of abundance index to this species is beneficial for its exploitation and utilization. In this study, based on the biomass data of the Pacific-cohort of Scomber japonicus during 1987–2012 obtained from Japan Fisheries Institution, as well as the marine environmental data and climatic data of spawning ground and fishing ground, we analyzed the relationship between the environmental and climatic factors and the biomass of this cohort. The significant factors were selected and the forecast models were established by using the generalized addictive models (GAM). The result shows the significant factors affecting the biomass of this cohort conclude the Arctic Oscillation index (AOI), Pacific Decadal Oscillation index (PDOI) and sea surface height (SSH2), sea surface salinity (SSS2) and sea surface temperature (SST2) both in the fishing ground. Result based on Akaike’s Information Criterion (AIC) suggests that the model 1 which included AOI, SSH2 and SST2 has the optimal model impacts. The model 1 passes the significant test (P<0.05) and the t test (P<0.05) is also passed based the validation result of model 1. Therefore, we suggest that this model can be used to forecast the abundance of the Pacific-cohort of Scomber japonicus.