Abstract： Objective　To estimate the internal exposure dose and the inhalation risk of radioactive aerosol to the submariners and offer some health protection parameters for the designing of new type submarine. Methods　Air samples from the submarine cabins were taken by DK-2A air sampler and the concentrations of the radioactive aerosol were measured by means of α、β radioactive counting; and the particle size distribution of the radioactive aerosol in the Ⅲ and Ⅴ cabins were determined by the WM-2 cascade impactor. Results　The concentration of the aerosol increased progressively in the submarine during under sea navigation. The mean particle size of the aerosol′s activity medium aerodynamic diameter(AMAD) was (0.22±0.02) μm and that of geometric standard deviation(σg) was(2.57±0.25). Conclusions　The navigatation time of submarine under sea is the main factor influencing the internal exposure dose of the submariners. The aerosol particle spectrum is consisted of some dispersed phases of small size particle whose distribution is narrow and is hazardous for inhalation. There is no relation ship between the particle size distribution of the aerosol and its concentration change.