You have to know what exactly his problem is, in order to help him out of the problem.
There are several possible causes of excessive eye blinking. Check which situation your son is in, according to his symptoms.
First of all, excessive blinking is a sign of anxiety. When a person is under stress, he or she may blink without self-consciousness. Talk with your son and try to figure out if something is bothering him. If so, try to communicate with him and reduce his anxiety.
Secondly, uncontrollable blinking is also a sign of eye allergy. If he is allergic to something, you need to keep him away from the allergen. Allergic rhinitis also cause allergies in eyes sometimes. Have him take some anti-allergic medicine.
Thirdly, the eyes may blink to soothe or relieve the irritation which is caused by infection.See if he has other symptoms of conjunctivitis like redness, itchiness, eye discharge or pain. If so, he may be suffering from conjunctivitis. In this case, you can give hot compresses or antibiotic eyedrops to his eyes to relieve the problem.
Lastly, take him to have his optical nerves examined if he doesn't have the problems above. It may be related to his optical nerves. In this case, he may also feel muscle pain or strain.