So, I tried to verify repomd.xml manually, the result is:
$gpg --list-keys
$gpg --import /etc/pki/rpm-gpg/RPM-GPG-KEY-
fedora-26-x86_64
gpg: key 64DAB85D: public key "Fedora 26 Primary (26) <fedora-26-primary@fedoraproject.org>" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
$gpg --list-keys
/home/rlu/.gnupg/pubring.gpg
----------------------------
pub 4096R/64DAB85D 2016-09-09
uid Fedora 26 Primary (26) <fedora-26-primary@fedoraproject.org>
$gpg --verify repomd.xml.asc repomd.xml
gpg: Signature made Sat 25 Mar 2017 02:41:50 AM CST using RSA key ID 64DAB85D
gpg: Good signature from "Fedora 26 Primary (26) <fedora-26-primary@fedoraproject.org>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: E641 850B 77DF 4353 78D1 D7E2 812A 6B4B 64DA B85D
I think this is a success result.
But why dnf is failed?
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