When intelligent electronic devices are connected to Ethernet of substation automation system in line with the IEC 61850 communication standard， implementation of TCP/IP protocol stack is a key technology. In order to adapt to software and hardware surroundings of the embedded system and meet its actual requirement， the standard TCP/IP protocol stack need to partly cut and modified， meanwhile， an embedded TCP/IP protocol stack suitable for 32 bits MCU is designed. The new protocol stack not only realizes the main functions of the standard TCP/IP stack， but also occupies fewer system resources. In addition， it is able to provide technologic support for the networking of intelligent electronic devices.