CST calculate impedance

I want to calculate the variation aperture impedance for the open-ended waveguide with frequency. How can I make it?

There is tab available on the top of CST main window which will calculate Q and losses for you.
Be sure to define proper material for model.
I am not able to understand your problem correctly as from question it seems that you want to do something to note the effect of change of aperture of waveguide if you explain a bit more then it would be easy to answer. But I think you want to see the insertion loss of waveguide for a particular aperture on certain frequency range. If it is the problem then you can very easily do it it with S parameter solver of CST by proper definition of ports

thanks for your attention.
i think it's better to send you reference paper. page 5 of it contains aperture admittance. I define waveguide port by putting a vacume sheet at the end of the structure without posts and calculate Z from S22 parameter but my result differs from paper. how can I send you paper (here or at email? )

I can suggest you one way out take screenshot of paper and attach it as image that will work.
What you mean when you are saying structure without posts?

the figure of structure and its aperture admittance attached here. the posts are shown in figure 6

fine it is like a stub tuner your attacking approach is perfectly fine and using S matrix you can calculate the impedance. Few reasons that could be for the difference in results
1. Material make sure that you have chosen the same type of material for simulation
2. CST uses default excitation signals for excitation of ports and that situation could be different if results presented in the paper are from some measured data