Abstract: The diagnostic equatorial port 12 (EQ#12) of the International Thermonuclear Experimental Reactor (ITER) integrates plasma diagnostic systems for observing and providing feedback on plasma operating conditions. Therefore, the integrated design of In-VV (vacuum vessel) area needs to consider important factors such as material out-gassing performance and port cooling capacity under the premise of port weight limitation and nuclear shielding requirements. Based on the standardized integration concept of EQ#12 In-VV area, the boron carbide (B₄C) shielding block was prepared by hot-pressing process, and its basic properties (such as microscopic morphology, physical and chemical properties), vacuum out-gassing characteristics and heat transfer characteristics under actual conditions were studied by SEM, mass spectrometry, symmetrical structure constant conductance method, steady-state heat flow method and finite element analysis. The results indicated that the density of B₄C shielding block under this hot-pressing process is (2.50±0.01) g/cm³, with few internal micro-pores. The total boron content reaches 77.20% and the content of impurity elements such as Fe and Co are not more than 0.03%. After baking treatment under vacuum conditions, the main gas composition released by the block is hydrogen and the out-gassing rate per unit area of hydrogen is as low as 6.94×10⁻⁹ Pa·m³·s⁻¹·m⁻². The thermal contact conductance of B₄C and stainless steel under vacuum condition (approximately 10⁻³ Pa) was tested at 100-500 ℃ and 1 MPa interfacial pressure. According to the test results, the thermal simulation analysis of B₄C under the application condition shows that it can effectively take away nuclear heat under the operating conditions of ITER device and the local maximum temperature will not exceed 221.6 ℃, also it can be heated to 209.1 ℃ for effective degassing after 48 hours of baking. The study on the application characteristics of this hot-pressing B₄C block material provides an important reference for the selection of shielding materials in the vacuum chamber of nuclear fusion devices.