If you turn off Photo Stream in iPhoto, the following happens:
Photos are removed from the Photo Stream view in iPhoto.
New photos taken with iOS devices in your Photo Stream continue to be uploaded to iCloud, but aren’t pushed to iPhoto.
New photos you import into iPhoto no longer appear on the iOS devices in your Photo Stream.
Your Photo Stream photos remain in iCloud for 30 days, and then they’re removed automatically. If you turn Photo Stream back on in iPhoto, any photos that haven’t been removed reappear in the Photo Stream view in iPhoto.
Your Photo Stream photos continue to appear on your iOS device until the photos are removed from iCloud, unless you turn off Photo Stream on the device.
To turn off Photo Stream in iPhoto:
Choose iPhoto > Preferences, and then click Photo Stream.
Deselect Enable Photo Stream, and then click Turn Off.
To turn off Photo Stream on an iOS device:
WARNING: Turning off Photo Stream on an iOS device removes all Photo Stream photos from the device, except for photos that have been saved to the device’s Camera Roll or to an album.
On your device’s Home screen, tap Settings, and then tap Photos.
Tap the Photo Stream switch to Off.
If you turn off Photo Stream on a device but don’t turn it off in iPhoto, Photo Stream continues to work with iPhoto and your other devices.