In order to enhance the experimental ability of the critical device, the ancillary buildings was extended beside the critical experiment hall. The ancillary buildings can’t significantly reduce the hall original containment . In view of the large non-standard equipment installation problem, the construction sequence was adjusted based on the the conventional construction process . The new containment technology was adopted,such as the planting bar technology, embeding steel plate, and using the wall, beam, plate integral pouring to construct process. After the end of construction, using SF₆ tracer gas method to test the containment of the critical device experimental hall and its ancillary building, the results show that, in the 24h SF₆ tracer gas accumulated leakage rate of 1.73%, the whole building meet the containment. For the important nuclear sites and the sealing places, the containment technology can learn from.