A powder velocity diagnostic system in ElectroThermal Chemical Spray (ETCS) coating technology has been developed. The powder velocity is a crucial variable that influences the coating quality. However, non-of the existing methods is suitable for the velocity measurement in the special conditions of the ETCS technology. The proposed diagnostic system is based on a familiar technique called Double Rotating Disk. It measures the powder particle time-of-flight between two parallel disks. The disks are rotated by a high-speed motor. The front disk has holes distributed on its circumference. Particles passing a hole are deposited on the second disk. The displacement between the position of the deposited particles spot center and projection of the hole center on the second disk is inversely proportional to the velocity. The method allows the measurement of particle velocity with accuracy better than 10%. The results are in a good agreement with theoretical model predictions. The method is able, also, to observe the powder deposition rate and the particles spatial distribution inside the powder cloud according to their dimensions as a function of time during the coating process.