Combining scattering theory and principle of SAR, a novel prediction model is proposed based on the multi-path scattering characteristics in the SAR image of cylinder tanks, for both the fixed and the floating top styles. The model can provide the relationship between the geometry parameters of the tank, the SAR parameters, the approximated position, and the scatting strength of the bright region in the SAR image. The validity of this model is proved by analyzing the Terra-SAR data and simulation experiments. Furthermore, geometry extraction is successfully implemented on the Terra-SAR data. The results show that the model is better than traditional methods in precision and stability.