In consideration of the importance of phonetic system, the oral broadcasting systems have appeared in more and more places such as subways, bus stations and supermarkets and so on. The aim of this paper is to introduce a high performance speech decoding system based on Cortex. On the basis of introduction to each part, the function of main chip has been described in detailed. The interface of main chips has been defined. The software structure is also discussed. The system adopting Cortex as microprocessor, 5605 as the MP3 decoder chip, can decode MP3 and WMA files stored in SD card. Equipped with a character LCD display module, the system performance has greatly improved by using Cortex processor.