Dry matter production and partition are the bases of yield formation of sweet peppers. In order to quantitatively investigate the effects of plant densities on the dry matter production and partition of sweet peppers, a model was developed for the decision support to optimize the crop and environmental management in solar greenhouse. Experiments with different plant densities and planting dates were conducted in a solar greenhouse from November 2007 to May 2009 in Shouguang region of Shandong Province (36°53′N, 118°43′E, 30.2m asl), wherein environmental and plant data were collected and analyzed. Results indicated that there is a logistic relationship between leaf area index (LAI) and the number of days after the planting date of sweet peppers at the plant densities of 2.0-6.7 plants m-2, and the maximum leaf area index at the harvesting date was relevant to the planting densities. There was a positive linear correlation between the crop biomass per unit area and the daily integral of photosynthetic active radiation (PAR) intercepted by the canopy. The dry matter partition index (DMPI) in leaves (fruits) increased (decreased) with the increasing density, and there was no significant effect of intensity on the stem DMPI. The harvest index related linearly to the corresponding accumulated daily integral canopy-trapped PAR. Therefore, the effects of plant densities on the canopy LAI and the light intercepted by canopy were quantified. Then a daily-scale model of solar greenhouse-grown sweet pepper was established to simulate the dry matter production and partition based on the integral PAR. The model was validated according to the independent experimental data and showed good performance. The determination coefficients (R2) between the simulations and measurements for the dry weight of whole plant, leaves, stems, fruits and yield were 0.946, 0.891, 0.945, 0.923 and 0.867 at the intensity of 2.0, 4.0 and 6.7 plant m-2 respectively, with RMSE 51.97g m-2, 3.53g plant-1, 4.72g plant-1, 16.4g plant -1 and 910.8g m-2. The precision in dry weight prediction for single-plant leaves was lower than those of stem and fruits, because leaves at lower levels turnd yellow and dropped off earlier, which cannot be simulated accurately. Marked by fewer parameters, higher precision and stronger applicability, the model can simulate the dry matter partition and prediction of the crop yield under sufficient water and fertilizer supply, and will provide decision-making support to the photo-temperature control management for sweet peppers in solar greenhouse.