After I unstalled a system app (guvera music) using es file explorer, its .dex file still exist in the /data/dalvik-cache/arm folder even after restarted my phone. Why Android is not smart enough to detect the change and remove it？Can I manually delete it to save space？FYI, the phone use rooted Android 5.0.
If you removed a system app without notifying PackageInstaller (which is often the case), the Dalvik cache won't be removed automatically. You of course can manually delete it to save space. It's 100% safe to delete Dalvik cache for a removed app.