In order for a Ghost Fluid Method (GFM) [1, 2] based method to work correctly and consistently, the influence of wave interaction at the material interface and the effect of material properties on the interfacial status have to be faithfully taken into account in the definition of the ghost fluid status.As such, utilising the two non-linear characteristic equations intersecting at the interface, a multi-medium Riemann problem can be defined and solved approximately to predict the ghost fluid states and thus led to the development of the modified GFM (MGFM) [3, 4].In this work, a mathematical model is proposed to analyze the various GFM-based approaches in literature.Under this model, a multimedium Riemann problem is separated into two single medium GFM Riemann problems, and the local truncation errors for various GFM-based approaches can then be analyzed.Error estimates [6] show that the MGFM indeed works far more effectively than the original GFM.With the help of this model, the MGFM can also be easily extended to treat fluid-structure coupling.Both theoretical analysis and numerical tests supported that the MGFM is a simple, flexible and robust way of treating fluid-structure coupling.