Sources of electricity in Malaysia are highly depending on fuel, natural gas and coal and desalination plant as for brackish water consume high electricity to produce freshwater. Ocean Thermal Energy Conversion (OTEC) and the Low Temperature Thermal Desalination (LTTD) plant is one of the mediums that will reduce these problems. This paper presents a simulation of the OTEC plant, LTTD plant and the Integrated OTEC plant using temperature and topographic characteristic information in Malaysia. The design optimization was also preferable in this study which affected and influenced the maximum output of power generation and freshwater production at maximum net power generation based on tropical data in Malaysia. A model for calculation and optimization is presented in this paper.