Abstract: The instrument and its working principle used in analogue and digital observation of radon are introduced, and the dynamic characteristics of digital radon data for Changli Well, Huailai 4th Well and Fanshan Well are analyzed in comparison with analogue data.The analysis shows that the work principle and observation steps of the two kind instruments are basically the same, but there are some differences in the sampling course (collecting gas).The gas sampling in analogue observation is performed artificially, but it is performed automatically by the instrument in digital observation.The difference in gas sampling affects the short cycle characteristics of the data, but their tendency are basically consistent.