In this study, based on 55 years’ worth of high-resolution simulated wave data using numerical modeling off the southern coasts of China, intra-annual and decadal variations of the wave climate and wave energy were evaluated. The results show that it is important to consider a sufficiently long time period for wave energy assessment to take into account the changing climate. The high-resolution wave dataset enabled the quantitative analysis in both nearshore and offshore, and the quantitative analysis was performed in two phases: First, using two different approaches. i.e., “Climate-dependent Sustainability Index” and “Wave Exploitability Index”, the wave power and its short and long-term changes were considered to prioritize the candidate stations for further assessment. Then, a modified “Multi-Criteria Approach” consisting of both sea state and Wave Energy Converters (WECs) was applied to determine the most suitable combination of WEC and location in the domain, which is Wave Dragon in the eastern parts of the domain with the energy production of around 92,000 MWh for a single device. The results provide the quantitative analysis for different scenarios of development plans in the study area on the selection of appropriate location and technology.