In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. There is a rectangular and a circular cross-sectional shape on the cold spray nozzle. It has been reported that the rectangular nozzle provides a more uniform particle velocity across the exit of the nozzle. The circular exit nozzle is parabolic in shape. So, spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle in order to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviors of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. We have studied copper particles so far. In this study, we will examine aluminum particles. First, we investigate the influence of the size and shape of the rectangular section nozzle on the velocity, temperature, and particle distribution of aluminum particles by CFD. After that, the rectangular section nozzles were fabricated and coating formation experiments were conducted, spray patterns and coating cross-sectional structures were observed, and coating adhesion was also evaluated. The nozzle material was polybenzimidazole (PBI) resin, which is difficult for aluminum particles to attach to nozzle walls. Plastic nozzles also limit the maximum allowable the working gas temperature, so this time it was set to 300 ° C.