Abstract: The blanket shield blocks is an important part of the International Thermonuclear Experimental Reactor (ITER). In order to ensure its sealing performance, each shield block needs to be taken a vacuum hot Helium leak testing. A method for high-sensitivity examination using a vacuum thermal helium leak test system was proposed in this paper. The shield blocks can remove its own impurity gas to avoid interference and increase the activity of Helium atoms by increasing the environment temperature. The examination sensitivity was improved by increasing the pressure difference between the inside and outside of the shield block. The sensitivity of this method can realize the helium leak test with the system sensitivity of 10^-11 Pa ·m³ ·s^-1 orders of magnitude under the conditions of examination environment temperature of 250℃, ambient pressure of 1×10-5 Pa, and products internal helium pressure of 4 MPa.The results indicated that the technology hada high degree of automation and data traceability, which can avoid the influence of the product's own outgassing on the examination, and had high sensitivity to the examination of subtle air leakage.