while installing os for my macbook pro it says like that what do you think the problem is"an internal error occured while preflighting your volume for APFS conversion"

It could be any number of problems. The simplest one is an HDD that is too full and does not have enough free space for the conversion. Boot it normally and check how much free space is on the HDD (I assume it's an HDD). And BTW, what version of macOS is currently on the machine?

Pls. report back here the size of your HDD and the amount of free space. If it's an SSD, that could be another matter, but report the same anyway.

It will also help to know the exact model MBP you have -- year, screen size, processor. You can get this information in About This Mac on your MBP.

Make sure to have a good backup before doing anything else in case you have a drive failure.

You can try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics don't detect most failures.