316L stainless steel powder was sprayed by a high-pressure HVOF process. Effects of powder size and the pressure in the combustion chamber on the velocity and temperature of sprayed particles were studied by using an optical instrument firstly at the substrate position. A strong negative correlation between the particle diameter and temperature was found whereas the correlation between the diameter and the velocity was not significant. The pressure in the combustion chamber affected the velocity of sprayed particles significantly whereas the particles' temperature remained largely unchanged. In-situ curvature measurement was employed in order to sturdy the process of stress generation during HVOF spraying. From the measured curvature changes, the intensity of peening action and the resultant compressive stress by HVOF sprayed particles were found to increase with the kinetic energy of the sprayed particles. The results were further used to estimate the stress distribution within the coatings.