The aims of this study were to investigate the habitat suitability and spatiotemporal variations of Hexagrammos otakii in the coastal waters of Dalian, identify the relationship between its resources and environmental factors, and provide a basis for habitat conservation and the selection of its release areas. Based on fishery survey data collected from May to October during 2015–2023, this study investigated the habitat suitability using synchronously-obtained sea-bottom environmental factors, including depth, temperature, salinity, dissolved oxygen, and chlorophyll-a concentration. A single-factor suitability index was established by combining the catch abundance of H. otakii (as a dependent variable) and five environmental factors (as independent variables) to analyze the relationship between the distribution of suitable habitats and environmental factors. A habitat suitability index model was built for each month based on the weights of the environmental factors derived from a boosted regression tree model to explore the spatiotemporal variation in habitat suitability for H. otakii. The distribution of suitable habitats for H. otakii varied by month. In the Bohai Sea area near Dalian, suitable habitats induced a north-to-south migration from May to October. In the Yellow Sea area near Dalian, suitable habitats induced H. otakii migration from nearshore to offshore and from west to east toward the waters around the Dachangshan and Haiyang islands from May to July, and then they reversed their migration back to the nearshore areas of southern Dalian City and Lvshun from August to October. Overall, the area of suitable habitats for H. otakii in the Yellow Sea near Dalian and its proportion within the studied sea area were higher than those in the Bohai Sea. This study explored the distribution and changes in the habitats of H. otakii, the optimal release times, and suitable waters for their release. These findings provide a scientific basis for the conservation and enhancement of H. otakii resources and to optimize stock enhancement strategies.