but i have used Mobi_unpack to unpack my mobi files its html is ok
Quite frankly, it's not "OK". The raw markup contained in your mobi is quite invalid (for MOBIPOCKET).
Use calibre or kindlegen to convert your source material to a MOBI. Then use Mobi_Unpack to examine the raw markup they
produce as compared to the raw markup in your
mobi. The difference will be quite apparent. MOBI-markup is more akin to HTML3.2 -- all inline attributes and no styles/classes.