I have a foreign bank account, but the deposit number is less than 10 thousand dollars. Do I need to tell the IRS this condition?

No, not as long as it did not exceed $10,000 at any time during 2016. 

The Bank Secrecy Act requires U.S. persons who own a foreign bank account, brokerage account, mutual fund, unit trust, or other financial account to file a Form TD F 90-22.1, Report of Foreign Bank and Financial Authority (FBAR), if:

1. The person has financial interest in, signature authority, or other authority over one or more accounts in a foreign country, and
2. The aggregate value of all foreign financial accounts exceeds $10,000 at any time during the calendar year.

Do this means I need to tell I have a foreign bank account ,although I don't need to file TD F 90-22.1 to report?

This means you only have to report the foreign bank account IF it exceeds $10,000USD at anytime in 2016. If it did not, then you do not have to report anything on the FBAR TD F90-22.1

Thank you!