Functional-structural plant modeling (FSPM) represents plant growth and development faithful to biology. After having established the functional-structural connection via allometry, the pattern of biomass allocation among individual organs is essential for FSPM. Currently the organ level allocation is based on mathematical equations, lacking detailed experimental data basis. In this study, we investigated relationships in relation to biomass allocation based on the datasets from two field experiments under different water regimes and plant densities. Data of leaf and internode biomass accumulation were collected by sampling at 2–3 day intervals in 2006–07 and 2009 field trials. Interplant competition did not affect organ initiation rate, which marks the starting point of new organs into biomass allocation while it is not determined for drought stress due to insufficient data. Drought stress and interplant competition reduced biomass accumulation of laminae, sheaths and internodes compartments. The biomass ratio between sheaths and laminae was not affected by drought stress and interplant competition, but the biomass ratios between internodes and laminae was affected. Overall, this study identified some findings for modelling biomass allocation into individual growing organs in maize.