With the rapid development of social economy and urbanization, urban spatial resources are becoming increasingly strained, making the gradual exploitation and utilization of urban underground space an urgent necessity. Assessing the suitability of such development is a critical first step. Coastal cities, being economic powerhouses and key nodes for external communication, have a more pressing need for urban spatial resources. Additionally, due to the complex influences of the marine environment, the suitability evaluation of underground space development in these cities is both intricate and essential. This paper focuses on the coastal area of Weibei Plain in Weifang City as its research background. It employs four different combined subjective-objective weighting methods of the improved structural CRITIC, game theory, minimum relative information entropy, and multiplicative synthesis method to empower. Based on the spatial analysis function of ArcGIS, it carries out a comprehensive suitability evaluation and comparative analysis of the underground space development in the research area. The results demonstrate:(1) Regardless of which combined subjective-objective weighting method is used, the outcomes consistently indicate that tectonic fractures, groundwater abundance, groundwater depth, and soil-rock layer permeability significantly impact the suitability evaluation of underground space development in coastal cities. (2) the improved structural CRITIC, game theory, minimum relative information entropy exhibit strong correlations, with correlation coefficients of 0.9825, 0.9585, and 0.9093 respectively. These methods scientifically reflect the subjective and objective weights of the various evaluation indexs. (3) In the evaluation results of the suitability of underground space development of coastal cities based on different combination weighting methods, the sum of very suitable and relatively suitable areas accounted for 44.13%, 42.87%, 41.35% and 42.53% of the total area, respectively.(4) Regions found to be very suitable for underground space development are primarily situated in the Shuangwangcheng Ecological Economic Zone in Shouguang City, the western part of Yingli Town, the central area of Gutidi Street in Hanting District, the western section of Zhuli Street, and the intersections of Longchi Street, Kuiju Street, and Duchang Street in Changyi City.