I have tow VMs, one CentOS 6.5 and another CentOS 6.8.
When creating the VMs, two network cards are assigned but the result is not expected.

The CentOS 6.5 VM have two IPs, but there is only one configuration file "ifcfg-eth0" in /etc/sysconfig/network-scripts
The CentOS 6.8 VM have only one IP and one "ifcfg-eth0".

I make another CentOS 6.8 image and create VM. In the new CentOS 6.8 image, several "ifcfg-ethX" is created manually.As a result, the new VM have two IPs.

I get question：
1、why the CentOS 6.5 VM have two IPs but only one network configuraion file "ifcfg-eth0"?
2、why the CentOS 6.8 failed to get multiple IPs until several "ifcfg-ethX" file created?

You say you have tow (two, I presume) VMs. What hypervisor are you using? How did you create them? How did you configure them, in particular what resources did you allocate to them?

FYI: Ip addresses require that a (at least virtual) network device exist, but a single device MAY be allocated multiple addresses. Not saying that is going on here, just that you have provided FAR too little information to convince either way. We need more complete data.