From 2016.05.12, the EternalBlue exploit attacks the 445 port vulnerability in windows systems worldwide, Will my 445 port still exposed if I connect windows machine to the Internet by an android phone's hotspot/tethering nerwork?
This depends on how you connect it. If you connect to a network Windows gives you the option to decide what kind of network this is. If you choose that you are on a public network (which is usually the default) then the SMB services will not be exposed to the network. But if you chose private network instead they will.
Note that exposing this port to the Android phone does not necessarily mean that it is exposed to the internet. As korockinout13 correctly says in his answer the phone will do NAT which means that the port will not be directly reachable from outside. But, the port will still be reachable from the local network, i.e. from any other systems connected to the same hotspot. This means that if any of the systems connected to the hotspot is already infected the attack might spread from this system to your system.
Your phone acts as a router with NAT during tethering, meaning that your computer is not directly visible or exposed to others on the internet. Even if you were to enable some kind of port forwarding on the phone, the carrier's network configuration would likely prevent it from being publicly accessible.
However, you could still run a malicious file that communicates with the service locally, or perhaps an attacker could craft a webpage that tries to talk to the port.
Short of your adversary being connected to your phone's hotspot or tricking you, you are safe from a random attack over the internet.