Cold spray (CS) is one of the thermal spraying methods which make coatings by spraying melted minute particles on substrate surfaces. Solid particles are sprayed onto a substrate at high speed to form a coating accelerated by a supersonic gas flow using a convergent-divergent nozzle. Therefore, it is important to understand the gas flow condition inside the nozzle that accelerated the gas flow. However, diagnosing internal gas flow is almost impossible for commercial CS nozzles because the nozzle is fabricated with hard metal alloy to prevent abrasions of the nozzle. Therefore, it is impractical to drill pressure taps to the CS nozzle to diagnose the gas flow. To solve this problem, authors propose non-intrusive flow-diagnostic methods which uses outer surface temperature of the CS nozzle and temperature recovery factor of the working gas. This research shows that the accuracy of this method is improved by measuring the outer surface temperature of the entire axial direction of the nozzle, and that the temperature recovery factor of the internal flow depends on the stagnation pressure. Therefore, the temperature recovery factor of the internal flow should be treated as a function of stagnation pressure.