I use iPad Air. How can I remove blank weeks between months on calendar?

You don't. The built in app is how it is. If you'd like to have it be differently then your best work around is to look for a third party calendar app that may have the ability to alter its lay out.

Ajstribunal wrote:

TThanks. This answered question, but not slightly confusing(towards the end of each month)problem.

perhaps Apple will address the issue.

I Look forward to update!

Based on what has already been announced, there's no reason to believe the next update will address this.

Submit your feedback to Apple requesting such a feature here:

http://www.apple.com/feedback

Meanwhile, there are thousands of calendar apps available in the app store. I'm sure that you could find one that you find less confusing. All the calendar apps use the same database so you wouldn't need to enter your data again.