Plant growth interpretation in term of accumulated intercepted solar radiation and the efficiency which the energy is used for dry matter production. This factor is used to the study of the growth and analysis of a wide variety of plant species in various environment. A number of crop growth simulation models have been developed using the radiation use efficiency (RUE) concept to forecast crop growth and yield in different environments. These models generally calculate daily biomass production as the product of the quantity of radiation intercepted and RUE. Research was carried out to quantify the RUE, biomass and leaf area index on Jatropha (Jatropha curcas L.) under rainfall condition, four levels nitrogen fertilizer (N) and two–tree levels population density (P). Experiments using a systematic Nelder fan design with 9 spokes and 4 – 5 radians were conducted on SEAMEO-BIOTROP field experiment in 2007. Data from the first experiment were used for parameterization and validation and data from the second further independent experiment were taken for the next validation purposes. The parameterization data set the average radiation intensity varied substantially from about 2.2 to 14.9 MJm-2d-1. Values of RUE at treatment W1N0, W1N1, W1N2, and W1N3 were obtained is 0.58 (r=0.85) g MJ-1, 0.66 (r=0.75) g MJ-1, 0.94 (r=0.82) g MJ-1 to 0.90 (r=0.76) g MJ-1 and for W1P1 and W1P2 were 1.3 (r=0.76) and 0.24 (r=0.76), respectively. Based on parameterization and evaluation, we suggest Jatropha models that rely on RUE for above ground biomass accumulation should be using a value of at least 0.94 (r=0.83) g MJ-1 to 1.3 (r=0.75) g MJ-1 for predicting optimum Jatropha growth. Validation between model prediction and field experiment show that model can simulate crop growth and development of Jatropha. KEYWORDS: radiation use efficiency, crop modeling, Jatropha