Many indeterminate plants can have wide fluctuations in the pattern of fruit set and harvest. Fruit set in these types of plants largely depends on the balance between source and sink strength within the plant. The fluctuation patterns in pepper fruit set and yield are a problem for the grower in the planning of activities throughout the production cycle. Functional-structural plant model(FSPM) can simulate plant growth from interactions among structural dynamics, external resources and the physiological processes that govern inter-organ competition using a source-sink concept. The source-sink concept is the major factor in the competition theory representing the supply and demand for assimilates. GreenLab, a FSPM, widely used to simulated plant growth and included algorithms to simulate a source-sink concept. Cyclic fluctuations in dry-matter allocation between organs occurred as a result of internal regulation simulated by the source-sink regulation concept. The feedback between organogenesis and photosynthesis is managed by the influence of the source-sink variable (Q/D) which controls plant development, especially fruit set and abortion, which is the main focus of this study. When the sink strength is high, due to many growing fruits and flowers, young fruits are not able to compete for assimilates with the fast-growing fruits and hence abort. Therefore, this study aims at investigating the fruit set pattern in a sweet pepper cultivar via source-sink relationships in FSPM GreenLab. A greenhouse experiment was conducted in The Netherlands (52°N) from April till September in 2007 for the sweet pepper cultivar ‘Funky’. Detailed destructive measurements on the dimensions and fresh biomass of above-ground plant organs for each phytomer were made throughout the season. Source and sink strength of each organ type were determined via the GreenLab model, with a description of plant organ weight and dimensions according to plant topological structure established from the measured data as inputs. Parameter optimization was determined using a generalized least square method for the entire growth cycle. The results indicate that the GreenLab model can simulate the fruiting position on the plant quite well. The Q/D evolution curves revealed two kinds of fruiting areas on the stem of the pepper plant. The deterministic behavior indicated the dominant fruiting areas according to the waves of Q/D and fruit set only occurred in these areas of the peaks of Q/D. Within the dominant fruiting areas, a probability occurred for whether a fruit set or not. The threshold of source-sink ratio on fruit set of 1.0 can reflect the temporal and spatial fruit set and abortion. The RMSE of the weights of fruits, leaf blades, leaf petioles and internodes were 15.3 g, 7.4 g, 4.8 g and 5.7 g respectively. As all the growing organs compete for biomass and fruit growth affects the growth of vegetative organs, temporal and spatial fruit set on the plant was simulated and feedback mechanism of fruit growth and growth of vegetative organs was studied. Via this theory, fruit set and abortion were randomly simulated, which is very similar with the behavior among plants grew in the real world. Such a model can be an output for each simulation time step and used to calculate precise light interception and energy balances for a single plant and stand in a greenhouse.