In industrial washing process, using chemicals causes increase of environmental load and processing costs. In this study, we focus on ice jet washing technology with ice particles generated in a converging-diverging nozzle. The purpose is to clarify the mechanism of the ice formation phenomena in the nozzle and to evaluate washing capability in ice jet washing technology. By visualization in the nozzle, we verified that shape of the nozzles was important factors to ice formation. Second, we constructed a numerical calculation system of quasi-one-dimensional stationary air single phase flow. It was indicated that a supersonic flow was formed in the diverging section and the pressure and temperature decreased in the ice formation area. Furthermore, a reverse pressure gradient was appeared with the generation of pseudo-shock waves and cooling of water was promoted. Finally, washing tests using fine particles simulated dirt was conducted and high washing capacity of the ice jet was verified. Improvement of washing efficiency was expected with the design of the optimal nozzle to ice generation.