A fiber grating based spectral-phase optical code-division-multiple-access (OCDMA) en/decoder was designed and realized. According to equivalent chirp theory, different frequency components of a broad band optical source can be separated and recombined by using step-sampling-chirped method, and phase shifts which carry address code can be introduced into these frequency components by an equivalent method. En-decoders fabricated by this method have some merits such as simple fabrication, low precision requirement. Therefore this method is suitable for system application. Comparison between computer simulation and measured data shows that the en/decoder has good performance.