DHCP can't dynamically assign IP adress
 

Now I install RedHat 7.2, Firstly 7.2 didn't recognize Ethernet Card, after installed the new driver (Intel Pro 1000 MT), 7.2 can find eth0, I can manually set IP address, but DHCp doesn't work. Need help.

i wouldn't recommend using such an old version of redhat, but the principles should still be the same. at the lowest level, to assign a DHCP addressing setup to a NIC, edit /etc/sysconfig/network-scripts/ifcfg-eth0 and set BOOTPROTO=DHCP rather than STATIC. there will be various higher level gui to do this, like netconfig.

I checked /etc/sysconfig/network-scripts/ifcfg-eth0, found BOOTPROTO=DHCP was already set, but miss DHCP_HOSTNMAE
item. Do I need add the machine hostname to DHCP_HOSTNMAE?

you don't need a dhcp hostname always, normally it's not needed. add one if youwant though. that should be all you need. so assuming that the interface IS eth0, starting the network script in /etc/init.d should go for dhcp. if not post what actually happens, maybe looking in /var/log/messages for info.