This study aimed to determine the effect of preheating AISI 316L metal substrate on the adhesion strength of the hydroxyapatite (HA) layer derived from green mussel shell waste deposit by the flame spray method. The deposition experiment was carried out in a spray gun with a distance of 10 mm with preheat of 200°C, 400°C, and 600°C. A sample without preheating was also a comparison. An optical microscope was for assessing the thickness and uniformity of the HA surface layer. The adhesion strength of the coatings followed the ASTM D4541 Standard. As a result, the adhesion strength of the HA coating increases with increasing preheat temperature. However, using Image-J software, at an initial heating temperature of 600 °C, the adhesion strength of the coating changed from adhesion- to adhesion-cohesive strength, leading to an increase in coating strength noted. The result can add knowledge to understanding the flame spray method for the HA-coated from green mussel shell waste on AISI 316L. The results obtained can increase knowledge to understand the method of flame spraying on HA-coated green mussel shell waste on AISI 316L. Preheat temperature, spray gun shooting distance, HA powder release, oxygen gas pressure, and LPG gas pressure can be used as references.