Significance: Radon(²²²Rn) is a naturally occurring radioactive noble gas. ²²²Rn is produced from the alpha decay of radium (²²⁶Ra), with a relatively long half-life (i.e., 3.8 days). Thus, ²²²Rn can diffuse and migrate from the rock and soil where it is generated and can enter the air. According to surveys conducted by the World Health Organization, exposure to ²²²Rn and its short-lived progeny is the second leading cause of lung cancer. The measurement and evaluation of ²²²Rn release involves not only occupational exposure but also public exposure. Therefore, the measurement of ²²²Rn exhalation and the dose assessments of ²²²Rn exposure have always been important concerns in radiation protection. Progress: The entire process of ²²²Rn moving from the soil to the atmosphere can be divided into three steps: emanation, migration, and exhalation. During the emanation process of ²²²Rn, ²²²Rn will obtain a recoil energy of 8.6 × 10⁴ eV from the decay of ²²⁶Ra, which will make ²²²Rn atoms travel through the soil grains at a distance of no more than 50 nm. If produced near the surface of soil grains, ²²²Rn will leave the grain and stop in the interstitial space (pore), becoming freely movable ²²²Rn. The fraction of freely movable ²²²Rn is usually expressed by the emanation coefficient (dimensionless). The emanation coefficient of soil generally ranges from 0.1 to 0.3. In soil with a relatively stable internal environment, the migration of free ²²²Rn in soil mainly relies on molecular diffusion caused by concentration gradients, eventually entering the atmosphere through the soil-air interface. If only diffusion transport is considered, then Fick's law can be used to describe the migration process of ²²²Rn and establish a model for ²²²Rn flux at the soil-air interface. The ²²²Rn exhalation rate at the soil surface is the ²²²Rn flux. On-site measurement methods of the soil ²²²Rn exhalation rate can generally be divided into three categories: accumulation, flow-through, and activated carbon adsorption methods. In actual measurements, different methods can be chosen according to the needs. Conclusions and Prospects: The understanding of the ²²²Rn diffusion exhalation mechanism and influencing factors is becoming comprehensive, and the measurement methods of the ²²²Rn exhalation rate for different purposes have been developed. Analyzing the physical processes of ²²²Rn exhalation from soil and measuring and evaluating the exhalation rate of ²²²Rn are important for assessing environmental radiation and managing uranium tailings and associated radioactive minerals. Moreover, the exhalation rate of ²²²Rn is closely related to the radiation environmental safety of on-site supervision of naturally occurring radioactive materials. Because of the complexity and diversity of ²²²Rn measurement sites, even though the amount of ²²²Rn release can be measured and calculated relatively accurately, nearly no quantitative deterministic correlation is detected between it and the indoor ²²²Rn concentration. Thus, the ²²²Rn exposure dose for key populations is difficult to estimate. The ²²²Rn exposure dose and health risks for key populations can only be estimated and controlled through measurements of the indoor ²²²Rn levels. Therefore, although the ²²²Rn exhalation rate is an important parameter that can be measured and calculated on-site, establishing a fixed exhalation rate limit for regulatory purposes is unsuitable.