Trachurus murphyi is a pelagic fish species, the resource abundance and distribution of which are significantly affected by variations in the marine environment. Accordingly, analyses of the influence of key environmental variables on the fishing grounds of T. murphyi are of particular importance in gaining an understanding of how fishing grounds are altered in response to changes in environment. In this study, we collected fishery data for Chilean T. murphyi from March to August, obtained during the period between 2013 and 2017, from the National distant-water fisheries data center of Shanghai Ocean University, along with data relating to the following 12 environmental factors: mixed layer depth (MLD), sea surface height (SSH), sea surface salinity (SSS), and water temperature at different depths (0, 25, 50, 100, 150, 200, 300, 400, and 500 m). Using these data, we examined monthly variations in the potential habitat of Trachurus murphyi based on a maximum entropy model. The key environmental factors in each month were selected according to the proportional contribution of each environmental variable, and the suitable range of key environmental factors was determined on the basis of the response curves of these factors. We also examined monthly variations in the key environmental variables. The results revealed that the spatial changes in potential habitat were essentially consistent with the actual fishing locations, and that habitat hotspots gradually shifted northward during the months from March to August. In March, the potential habitat hotspots were distributed in the waters between 42°S and 47°S, and extended to regions north of 30°S in August. The contribution of environmental variables in each month indicated monthly differences in the key environmental factors, as well as in the suitable environmental ranges. The key environmental factors were identified as Temp 400 m, Temp 500 m, and SST in March; Temp 400 m, Temp 500 m, and MLD in April; Temp 500 m, SST, and Temp 400 m in May; SST, Temp 500 m, and Temp 50 m in June; SST, Temp 300 m, and SSH in July; and SSH, Temp 300 m, and Temp 100 m in August. In addition, water temperature was identified as an important factor affecting the spatio–temporal distribution of the fishing grounds, and the suitable water temperature layer in different months was found to be consistent with the migration characteristics of T. murphyi. With the northward movement of the habitat, the contribution rate of SSH gradually increased, which may be related to the distribution of currents off the Chilean coast.