The relationship between agricultural ecological engineering and farming systems is discussed in this paper with a theoretical analysis and case study. The theory and approach of farming system design is implied in agricultural ecological engineering. Thus, farming system as a theory and approach of agro-ecological engineering plays a very important role in the management of agricultural systems. Farming systems are the bridge between agroecological engineering and agricultural systems. More comprehensive advanced research on farming system theory and approaches employing ecological principles are needed to achieve more productive sustainable agricultural systems. New terms on eco-economic unit and eco-economic niche are explained in the paper.