In order to investigate the DNA damage exposed to ultraviolet-C(UVC) and the effect both of detecting method and sample types on the result, the ,Bacillus subtilis, and general DNA were used as the model samples irradiated with different doses of UVC respectively. Subsequently, DNA fragments were analyzed by 8 h, 16 h, and 24h pulsed-field gel electrophoresis (PFGE). The result has been revealed that the 16 h PFGE could reflect the DNA double strand break (DSB) more exactly. With the analysis of 16 h PFGE map it has been found that the percent of DNA release increases gradually with the increment of radiation doses. What's more, the most DSB appear at the dose of 17.8 J/cm,2, in the thallic samples and at the dose of 72.7 J/cm,2, in the DNA samples. The DSB is more significant in the thalli than in general DNA. The results indicate that the DSB level induced by UVC is related with irradiation doses as well as sample types.