If my son is doing GED course, can he be considered as student and can I file him as a dependent?

If your son:

 - Was under the age of 24 on Dec 31 of the tax year and;
 - Was enrolled as a full time student for any one semester that started in the tax year, and;
 - Was enrolled at an accredited institution, and;
 - Was enrolled in a course of student that will lead to a degree or credentialed certification, and;
 - Did not provide more than 50% of ***HIS OWN SUPPORT*** for the entire tax year

Then

You qualify to claim the student as a dependent on your tax return.

Note that a GED is a "credentialed certification" so you're fine there. Now if "all" the above criteria are met, then it does not matter how much money your son earned during the tax year. Note also that 3rd party income received by your son such as scholarships and money from the parents, does not count for the student providing their own support.