Sorry, this is tracker for koji development not running instances. Is it in Fedora's koji?

In centos7

Give me link to that task, I can look at it a bit (It will probably need rel-eng action anyway).

Sorry, In my env, not Fedora's koji. I'm afraid that no link for you.

So, possible options:
1) is there some latest-build on the build tag? (Maybe it is in the package list but there is no real build behind)
2) Is there actual repository created? (Are you running kojira or regenerating repos manually?) You can try to check repodata if they contain the rpm or not. (or run 'koji regen-repo xyz')
3) There is really some dependency issue (unlikely) on rpm level.

I am afraid that python3-Cython srpm build out python34-Cython-0.28.5-1.el7.5es.x86_64.rpm and python36-Cython-0.28.5-1.el7.5es.x86_64.rpm.
So When I build, koji cannot find python3-Cython. It should be python34-Cython?

It depends on spec file. I would assume that it can provide just python34-Cython or maybe also python3-Cython and/or python-Cython.

Just try to get that build repo and play with that (e.g. via koji mock-config).

Enen, I find out. And to close it.
I build ceph rpm and it spec file depend on python3-Cython by this:

BuildRequires: python%{python3_version_nodots}-Cython # python3-Cython

My koji repo only has python34-Cython or python36-Cython
So i modify to:

BuildRequires:  python%{python3_pkgversion}-Cython  # python36-Cython

It works.
Tnanks

This issue has been migrated to Fedora Forge:
https://forge.fedoraproject.org/koji/koji/issues/2863

Please continue any further discussion there.