I change calibre-qui to calibre-tray in
self.system_tray_icon.setIcon(QIcon.fromTheme('calibre-gui', self.system_tray_icon.icon()))
and problem solved.
self.system_tray_icon.setIcon(QIcon.fromTheme('calibre-tray', self.system_tray_icon.icon()))
I change calibre-qui to calibre-tray in
self.system_ tray_icon. setIcon( QIcon.fromTheme ('calibre- gui', self.system_ tray_icon. icon()) )
and problem solved.
self.system_ tray_icon. setIcon( QIcon.fromTheme ('calibre- tray', self.system_ tray_icon. icon()) )