Plasma spraying ZrB2 ceramic coating is considered as potential candidate method of Thermal Protective System. While the application of plasma sprayed ZrB2 coating is restricted due to its oxidation. Therefore, it is important to study the oxidation behavior of the ZrB2 material. In this research, oxidation behavior of the ZrB2 ceramic, which achieve different density by using SPS and pressureless sintering, is studied to explain the oxidation behavior of plasma spraying ZrB2 ceramic coating. The oxidation behavior of ZrB2 ceramics is investigated using SEM, XRD and EDS. The ZrB2–based ceramic coating is gravely oxidized at 600°C, but the block ZrB2–based ceramics also possess excellent oxidation resistance above 1000°C. The density of ZrB2 ceramics significantly increase when changing the sintering method from pressureless sintering to SPS. The high density has beneficial effect to improve the oxidation resistance of ZrB2 ceramic, for there are few open pores channel in high density ceramics. The oxygen cannot diffuse to the inner through pores, as a result, the high density ceramics can only be oxidized from outside to inside progressively, unlike low density ceramics, whose surface and inner is oxidized simultaneously.