How to go to Hebei, which is the nearest international airport? How is the weather during September?

It depends on which city you are staying. Though, Shijiazhuang Airport and Beijing Capital Airport are the nearest ones.

In Sep. the whole province is still warm, with the average temp of around 22℃, but there will be a little bit large temp gap between daytime and night, so prepare a jacket. Cloudy days would mostly happen and there will also several lightly rainy days.