Objective To evaluate the distribution of DIAGNOdent value according to varying clinical caries severity. Methods A total of 541 deciduous molar teeth in children aged from 5 to 6 were examined using DIAGNOdent by one trained dentist. The most severity site in every tooth was recorded. The same sites were examined visually by another dentist. The distribution regular of DIAGNOdent value was analyzed according to the clinical severity score by Ekstrand index. Results The higher the visual score, the higher the mean DIAGNOdent value. The variation of values in each visual category was larger than that of values recommended by manufacturers. When clinical severity score was 0, 1, 2, 3 and 4, the median of DIAGNOdent value was 0, 5, 19, 49 and 99 respectively. The mean value for sound surfaces was lower in primary teeth than the cut-off points recommended by manufacturers, but the value of DIAGNOdent was increased obviously when the transparency change of enamel was detected visually. Conclusion DIAGNOdent is useful in detecting occlusal caries in deciduous teeth, but the cut-off levels is not coinciding perfectly with manufacturer suggesting.