The bar code is by one and empty different in width , parallel and adjoint of one group. Symbol made up according to certain code rule. Can represent such information as the letter , figure ,etc. Generally a bar code can hold the letter , digital information within 20 . 　Bar code technology is to study how to use the identification information of the bar code.. And change the information of the identification of the bar code into the language that a computer can discern. Make use of bar code technology to realize and discern automatically.