In order to investigate the relationship between the preparation process of FeCoCrNiMo high entropy alloy (HEA) coatings and the porosity of the coatings, as well as the differences between the microstructure and oxidation behavior of different coatings. We used the atmospheric plasma spraying (APS) process to prepare FeCoCrNiMo coatings and designed orthogonal tests to select coating specimens with different porosities. The microstructure and elemental composition of the coatings were observed by XRD physical phase analysis, SEM and EDS, and the differences in oxidation behavior of the different coatings were analyzed. It was found that the coating porosity was distributed between 2.85%~7.52% after optimization of the FeCoCrNiMo coating preparation process by orthogonal tests. The most representative 7.52% porosity (denoted as H1) and 2.85% porosity (denoted as H2) coatings were analyzed, both of which had a simple FCC structure with a typical lamellar microstructure and a significant distribution of oxide and HEA phases inside the coating. The oxidation behavior of FeCoCrNiMo coating follows the parabolic theorem, during the oxidation process, Cr, which is chemically active, is most likely to precipitate and generate oxides. The metal atoms that are desolvated mainly include Cr and a small portion of Ni that react with O. The element Mo, which has a large atomic diameter, has a low solubility in the HEA alloy phase due to the large difference in atomic size with other elements, and during the high temperature oxidation process, with the desolvation of Cr and Ni elements and the reduction of the lattice size of the two elements, it also precipitates out of the alloy phase and exists as a single mass in the in the coating. The H2 coating with lower porosity generates dense oxide layer faster and has lower oxidation mass growth rate, which is about 5.16 mg/cm2 after 15 h. The FeCoCrNiMo coating with lower porosity has better oxidation resistance, and the orthogonal test can be used to optimize the porosity of the coating effectively.