Abstract An isomorphism preserving Hamming weight between two algebraic geometry (AG) codes is presented to obtain the main parameters of Justesen s algebraic geometry (JAG) codes. To deduce a simple approach to the decoding algorithm, a code word in a "small" JAG code is used to correspond to error-locator polynomial. By this means, a simple decoding procedure and the ability of error correcting are explored obviously. The low and up bounds of the dimension of AG codes are also obtained.