Sacred lotus (Nelumbo nucifera) belongs to Nelumbonaceae family. Its seeds are widely consumed in Asia countries as snacks or even medicine. Besides the market values, lotus seed also plays crucial roles in lotus life cycle. Consequently, it is essential to gain a comprehensive understanding on the development of lotus seed. During its development, lotus seed undergoes cell division, expansion, reserve accumulation, desiccation and maturation phases. We observed the morphological and biochemical changes of lotus seed from 10 to 25 days after pollination (DAP) which was corresponding to the reserve synthesis and accumulation phase. The volume of the seed expanded until 20 DAP with the color of the seed coat changing from yellow-green to dark green and gradually faded again. Starch and protein rapidly accumulated from 15 to 20 DAP. To further reveal the metabolism adaptation, primary metabolites and proteins profiles were obtained from the mass spectrometry based platforms. Metabolites and enzymes involved in sugar metabolism, glycolysis, TCA cycle and amino acids metabolism schematized on their biosynthetic pathways. Both metabolic and proteomic profiles indicated more active metabolism from 10 to 15 DAP than after 20 DAP. The results provide a frame of reference for the evaluation of primary metabolism during lotus seed development.