This paper introduces the research background and current status of the airtightness test in the habitable zone of the main control room. The airtightness test in the habitable zone of the main control room is studied from multiple dimensions, including the selection of test methods, tracer gas injection and sampling methods, equilibrium concentration, and evaluation and calculation of test results. It has been improved and applied in the HPR1000 nuclear power plant; The results showed that by studying the factors affecting the uniformity of tracer gas mixing, the relationship between positive pressure and internal leakage was determined, and the ideal positive pressure value for conducting the experiment was obtained; By studying the relationship between positive pressure and air volume difference, the ideal positive pressure range for conducting the experiment was determined; On this basis, through comparative analysis of tracer gas concentration data, the fluctuation amplitude and regularity of concentration were analyzed, and effective measures to promote tracer balance were proposed, namely, increasing mixed flow equipment can make the tracer gas concentration fully uniform and reduce the fluctuation amplitude of concentration.