error : Showing Recent Issues ld: library not found for -lGTMSessionFetcher
Unity 2017.1.0f3
Google ios SDK 1.7
How can I solve the problem?

Did you open the .xcodeproj or .xcworkspace file?
open .xcworkspace锛孊ut now the error is reported

I can not repro this issue on Unity 2017.1.0f3. A blank project setup for cardboard (or a project with gvr-unity-sdk 1.7 sample scenes) builds and runs fine on iOS.
Can you provide a repro project or precise repro steps? A longer log might help as well to see what duplicate symbols are being reported.
We've updated the Get started with Google VR in Unity on iOS guide. The new guide includes a note about the importance of opening the generated *.xcworkspace file instead of the *.xcodeproj file.
@qiaonifengxue Please let us know (by filing a new issue) if you encounter any issues creating a working Xcode project using the latest Unity 5.6 or Unity 2017 and the latest Google VR SDK for Unity using the above guide.
Duplicate of #539
Most helpful comment
We've updated the Get started with Google VR in Unity on iOS guide. The new guide includes a note about the importance of opening the generated
*.xcworkspacefile instead of the*.xcodeprojfile.@qiaonifengxue Please let us know (by filing a new issue) if you encounter any issues creating a working Xcode project using the latest Unity 5.6 or Unity 2017 and the latest Google VR SDK for Unity using the above guide.