In order to study the growth behavior of greenhouse tomato with different density, GreenLab, the functional-structural model, was improved. On the basis of improving the degree of fitting, the growth parameter of tomato with different density was obtained. Environment was connected with tomato plant growth behavior through the analysis of the parameter. The results show that the density influences production and distribution of assimilate, which was characterized by the exterior morpha such as leaf appearance rate, leaf thickness, fruit set rate and so on, and GreenLab model can reproduce this feedback relationship. 