Vegetation plays an important role in the terrestrial ecosystems. Monitoring vegetation is of great importance in understanding the climate change. Passive microwave remote sensing behaves as an attractive technique due to its penetrability and comprehensive macro scale. It is of great significance to develop a good forward model with simple form and high accuracy for the inversion. The commonly used T-co model takes very simple form and is good for fast inversion. However, it is always limited at low frequency or for sparse vegetation. In this study, we present a parameterized model based on the Matrix Doubling (MD) model. The result shows that the parameterized model achieves rather accuracy with the theoretical MD model, and the RMSE is 0.0077 in V polarization and 0.018 in H polarization, and the correlation coefficient is above 95%.