By using solid-state nuclear detectors, the air radon concentrations at 87 underground working places were measured during spring, summer and winter, respectively. The survey covered 23 cities whose annual radon concentrations range from 14.9 to 246.4 Bq·m -3 with an overall arithmetic mean value of 106.7 Bq·m -3. The average annual effective dose received by people working in these underground working places was 1.6 mSv, hence the lifetime fatality risk was 1.2×10 -4. Fujian Province had the highest radon level during the survey. It is better to reduce the radon concentration heavily in summer because of higher radon concentration than in winter.