You can claim your ex-spouse as an exemption only if he meets all the following rules:

• Gross Income: He earns less than $4,050 in 2016.
• Total Support: You provide more than half of the total support for the year. - Support Test
• Member of Household or Relationship: He must live with you all year.
• He is not claimed by another taxpayer.

Your ex-spouse also needs to meet one of the followings:

1.  a U.S citizen / greencard holder, or 

2.  a national of U.S possession or

3.   a resident alien ( by meeting the  Substantial Presence Test  ) or 

4.  a resident of Canada or Mexico .