Numerous commercial fish populations have declined in recent years owing to the impacts of overfishing, climate change, environmental pollution, and other factors. However, the cephalopod fishery has continued to develop, including increasing harvests of Japanese squid Loliolus (Nipponololigo) japonica (Hoyle 1885). L. japonica plays an important role in the food web of the Haizhou Bay ecosystem, where it is a primary catch in bottom trawls and some net fishing. The species spawns in the bay and adjacent waters annually in early May, and it uses these waters as a nursery ground. Despite the ecological and economic importance of the species, few studies of its spatio-temporal patterns of distribution are available, and spatial autocorrelation of data is often lacking in the studies. Analysis of temporal and spatial heterogeneity in the distribution of L. japonica in Haizhou Bay and adjacent waters has significance for sustainable utilization and scientific management of this fishery. To study this, we used the survey data of bottom trawls in Haizhou Bay and adjacent waters, collected in 2011, 2013, 2014 and 2015, for spatial analysis of center of gravity and semivariogram plots to investigate temporal and spatial distribution of L. japonica resource density and average body size. The average mantle length of L. japonica was larger in spring than in autumn for each of the four sample years, and the average mantle lengths did not significantly differ (P>0.05) for spring, but did significantly differ for autumn, except in 2011 and 2013, 2013 and 2015. The L. japonica population was distributed throughout Haizhou Bay and its adjacent waters, and local distribution showed no correlation with size. In both spring and autumn, the dominant size class was 20-50 mm mantle length. The resource density of L. japonica differed significantly (P<0.05) between spring and autumn, except in 2013, and was greater in autumn than in spring. Center of gravity of the resource density changed in opposite directions between spring and autumn: squid were more concentrated in the autumn than in the spring of each year; yet in both seasons, the resource density was relatively centered in the middle of Haizhou Bay and adjacent waters; differences in center of gravity among the years and seasons were not significant. Spatial heterogeneity in resource density of L. japonica appeared to be caused less by randomness than by structural variations. The spatial distribution of L. japonica in the study area displayed a well-organized structure, with medium to strong spatial autocorrelation in 20-30 km.