The aim of the paper is to explore the deformation mechanism of particles in cold spray. Focused ion beam/ scanning electronic microscopy (FIB/SEM) system was employed to prepare a TEM specimen of a whole copper particle on aluminum substrate on wipe test. Through analyzing the microstructure of the TEM sample, the result indicates inhomogeneous deformation of Cu particles is due to inhomogeneity of stress field and temperature. During the impact, the kinetic energy of particles transformed to deformation energy and heat, which led to alumina layer broken and the temperature increasing quickly. Because of high temperature and strain rate, re-crystallization has happened in Cu near the interface and intermetallic compound Cu₉Al₄ has been obtained on the interface. The farther the grains were from the interface, the less influence happened on them. Grains had few effect of heat or stress field on the location far away from the interface, especially on the top of particle.