Thermal spraying is one of the successful surface processing method that gives restoration or a new function on various mechanical components. The thermal spraying process accelerates the solid particle by a high temperature and a high velocity gas stream. After impacting on the surface of the substrates, the particles are formed into a coating. The present study is a gas-dynamic research on a cold spray, which is a cutting edge coating method. The cold spray process makes the solid particle impact on the substrate at a high velocity by a supersonic gas flow in the state of the solid phase to form a coating. It is experimentally clarified that the particle starts deposition on the substrate when particle velocity exceeded a critical velocity. Therefore, it is important to clarify the particle behavior. In this study, the influence of the loading ratio on the gas flow and the particle behavior is examined by quasi-one-dimensional analysis that assumes two-way coupling. The calculated results reveal that the gas velocity and the particle velocity decrease as the loading ratio is increased.