Is there a way to check my husbands fertility without him knowing?

No: You need a sperm sample. It would be difficult to do this without his knowledge. Also you should ask yourself why you can not talk to him about such an important question.

No: If you two are serious and committed about seeking fertility treatment, then both of you should get evaluation by the doctors without any secrecy. An appropriate evaluation will require medical interview and the necessary labs/imaging tests.