The shortage of river sand and fresh water for concrete production has become a severe issue, accompanied by a significant increase in infrastructural constructions, especially for coastal areas. Therefore, the possibility of utilizing seawater and sea sand as alternative raw materials for concrete components has attracted broad research interest in recent decades. This paper presents experimental, and simulation investigation to comprehensively study the material performance of seawater fly ash cement paste (SFCP). An integrated simulation platform is adopted to achieve the performance assessment, in which the physicochemical and geochemical processes can be addressed, such as the hydration of cement particles, formation of micro-pore structure, multi-species migration and equilibria, activity effect, the thermodynamic balance between the matrix skeleton and pore solution. A comparison of experiment and simulation showed that the properties of SFCP from micro to macroscale are consistently associated and fairly explained through the integrated simulation platform for further practical realization.