Im using Lightroom 5 for a long time but it seems that lrcat file is gone for a while. Im relying on backup lrcat file but I need to re-create lrcat file for the entire files. Without it, I cant access to Lightroom unless I use recent backup lrcat file. How can I re-create lrcat file?
It's not clear what you are asking.
If you are "relying on a backup lrcat file", what does "relying" mean? Why aren't you using the original, and not the backup? Please provide more details.
I dont have original ircat file. It's gone.
Copy the backup .lrcat file to the original location the catalog file was in.
Lr catalog files don't just go missing for no reason. The reasons behind something like this happening is User Error, you deleted or moved the catalog file, or a hardware fault.