This text carries on the detailed comment to the composition and principle of MP3 player at first, then compare the present popular hard scheme of MP3 player. After analyzing , think that use the AT89C51SND1C chip that ATMEL Company produces as a master controller , flash memory chip of Samsung K9F5608 as memory, CS4330 for D/A is the best scheme. AT89C51SND1C is a 51core MCU that implement a MP3 decoding machine. This biggest advantage of scheme is that the circuit is relatively simple, only 3 chips. Take this scheme as an example , has introduced the design of the hardware circuit of MP3 player and systematic software design in detail , and carry on in-depth analysis to software design , improve the operational efficiency of the software. Programming software is the Keil uVision . The programming language selects high-efficient C51 language. Introduce the debugging software of MP3 player and debug the method finally. Built-in 64Kbyte FLASH ROM of AT89C51SND1C, it can wipe repeatedly and write 100,000 times. Downloading the firmware through the USB interface of AT89C51SND1C, it is very fast to download the firmware. The download software is FLIP, ATMEL Company grants software free.