In this study, the inter and intra-annual variation of wave energy in Southeast Asia is evaluated using 55 years of simulated wave dataset using JRA-55 wind field as forcing to SWAN numerical model with the boundary condition provided by a global wave model. The model was validated against the satellite data for monthly averages of significant wave height. After validation, the wave characteristics generated by the model for 55 years were used to calculate the wave power parameter, and time series of wave power in each output grid point were utilized to evaluate the inter and intra-annual variability of wave resources, as well as its decadal changes and its spatial distribution. The results of this study reveal novel information about the sustainability of available resources in long-term taking into account the decadal changes for the first time, and specifies the areas with higher stability for wave downscaling in order to determine the potential locations for wave energy extraction.