The bar code behind the jewelry label is read by a bar code reader. The bar code on the back of jewelry label has different reflectivity to light. Under the irradiation of the bar code reader, reflected light with different brightness is generated, which is received by the bar code reader, turned into electric signals with different heights, and then shaped to represent the high and low levels of digital signals. After the decoding circuit, the digital signal can be restored to the number or symbol represented by the bar code. So the bar code behind the jewelry label is read by the bar code reader.