The interaction of two or more tropical cyclones (TC) has been known for a long time as one of the more difficult challenges, in forecast as well as in research, in the Northwestern Pacific where such situation is most common. Detailed objective diagnosis and numerical simulations indicated that the intensities and movements of the related typhoons were influenced mutually as they presented in a certain region. Strength of the steeling flow, intensities and relative positions of the TCs are the major factors in considering this kind of problem. Many studies has been carried out but focused mainly on typhoon circulations. In this work we are not only, by using the NCAR/Penn State Fifth Generation Mesoscale Model (MM5), simulating the interaction between typhoons Saomai and Bopha but also do some controlled test. Results show that the MM5 is able to predict the tracks of the two typhoons well. And, as well, gives a reasonable result in the controlled run. In it, as we filled out typhoon Saomai, typhoon Bopha°¦s track shifted, mainly to the north, a certain amount. Furthermore, test showed that various processes such as cloud physics, cumulus parameterizations, and et al., have different effects on the interaction.