Abstract: The length of plasma jet was obtained on the basis of digital image processing and the CCD image gathering sy stem, and heating effect was determined through the temperature rising of a substrate in the unit time by an IR pyrometer.Then comparative experiments of heating effect by plasma jet and particle flux were carried out under different spray distances and lengths of plasma jet to analyze their characteristics.Experimental results show that when the length of plasma jet is shorter than or equal to the spray distance, heating effect is dominated by plasma jet.However, if the length is longer than the spray distance, the heating effect of particle flux becomes more and more obvious, but the case for plasma jet drops rapidly.Therefore, the length of plasma jet, as a characteristic evaluation index, can be adopted to select the reasonable spray distance. This is certified by the patterns and cross-section thickness profiles of deposited coatings under different spray distances.