Hi,
I am working for my parent company in NJ and my Indian company send me through L1B visa. Approximately my stay period is around 6 months to 1 year. Currently I am paid as Per diem in my Indian Account.

If My stay period is more than 6 months then I need to switch to US company pay role and pay tax to US Government ? Or can I continue with the indian per diem salary ?

Thanks in Advance.

After 183 days in the same tax year, your pay and per diem becomes taxable.

Yes, AtlantaTaxExpert is correct. Here is from the publication 901:
Income that residents of India receive for personal services performed in the United States as employees (dependent personal services) is exempt from U.S. income tax if the residents meet three requirements.
• They are present in the United States for no more than 183 days during the year.
• The income is paid by, or on behalf of, an employer who is not a resident of the United States.
• The income is not borne by a permanent establishment, fixed base, or trade or business the employer has in the United States.

Noted!