[en] FD-71 NaI(Tl) scintillation radiometer is a sensitive, simple and portable instrument. In preparation for surveying the external dose rate level due to natural background radiation in China, this instrument was investigated thoroughly. The characteristics, calibation methods, correction formula for readings and total error estimation for this radiometer are described in this paper. The detection capability of FD-71 radiometer is 0.5 ∼ 500 μR/h for terrestrial gamma radiation. The difference of readings between instruments is generally within 5% and the differences in reproduciblity and stability between instruments are within 3% and 5%, respectively. The results of the two methods for calibrating FD-71 radiometers, one using ²²⁶Ra and the other being field calibration, are approximately identical. For comparison, simultaneous in situ measurements were carried out using both FD-71 radiometers and RSS-111 high pressure ionization chamaers at 2,961 sites throughout China in different environmental mornitoring situations. The results showed that the difference between the two monitors was geaerally within 5 ∼ 10% with a maximum of 25%. The total error of FD-71 radiometers in common environmental background radiation field is within +- 12%