I just updates me system to the latest vision and I found out that the iPhotos' photo just totally lost. I do back up my photos normally but just through iPhotos. How can I or is it possible for me to get back my photos?!?! T.T
Open PHotos for the first time and it should ask if you want to migrate your iPhotos library. Read Get started with Photos for OS X - Apple Support
The only version if iPhoto that is working on El Capitan is iPhoto 9.6.1.
If you bought iPhoto from the AppStore you should be able to update to iPhoto 9.6.1 by reinstalling it as described in barney's user Tip:
Can't Update iPhoto because it is not available in the App Store
Even if you want to switch to the new Photos.app as recommended by rkaufmann87, try to update iPhoto. You may need it to repair your iPhoto Library or to open iPhoto projects.
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