Thanks for your reply,
I had fix this problem by change the autoneg setting from fause to true, then the link status can stably remain in the up state.
phy8201Config.autoNeg = true.
ESC phy chip is TI DP83848
But then ,I have met an other issue:
When the current EtherCAT master station's network port is directly connected to the slave station, the two cannot interact, and the slave station cannot go online. Later, when the network port of the master station environment in this demo was directly connected to the PC, it was found that the packets captured by the PC's network port were 19-byte packets with an ETH TYPE of 0x888E. However, if a HUB is first connected in series between the master station environment and the PC, the PC's network port can capture the correct EtherCAT packets (BWR & BRD) sent from the master station demo environment.