His English is very good. It helps him to study maths to a great level.
His English is very good. It helps him to study maths to a great degree.
I think both works!
Do you think the same as me?
Neither of them work well, because "great" is not the best adjective here. I think what you want to say is that his good English allows him to pursue his studies at a high level. "Degree" doesn't convey the right idea.