UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE
13a-16 OR 15d-16 UNDER
THE SECURITIES EXCHANGE ACT OF 1934

For the month of August 2021

Commission File Number 001-13314

Huaneng Power International, Inc.

(Translation of registrant’s name into English)

Huaneng Power International, Inc.

Huaneng Building,

6 Fuxingmennei Street,

Xicheng District,

Beijing, 100031 PRC

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.  Form 20-F  x Form 40-F  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ¨

This Form 6-K consists of:

An announcement regarding unusual movements in the trading of the A shares of Huaneng Power International, Inc.(the "Registrant"), made by the Registrant on August 24, 2021.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Hong Kong Exchanges and Clearing Limited and The Stock Exchange of Hong Kong Limited take no responsibility for the contents of this announcement, make no representation as to its accuracy or completeness and expressly disclaim any liability whatsoever for any loss howsoever arising from or in reliance upon the whole or any part of the contents of this announcement.

OVERSEAS REGULATORY ANNOUNCEMENT ANNOUNCEMENT
ON UNUSUAL MOVEMENTS IN THE TRADING OF
THE A SHARES

This overseas regulatory announcement is made by Huaneng Power International Inc. (hereinafter the “Company”) pursuant to Rule 13.10B of the Rules Governing the Listing of Securities on The Stock Exchange of Hong Kong Limited (the “Hong Kong Stock Exchange”).

Important Content:

The deviation value of the increase in the closing prices of the A Shares of the Company accumulated more than 20% in three consecutive trading days on 19th, 20th and 23rd August 2021, which reached the relevant required standards of the “Trading Rules of the Shanghai Stock Exchange” and constituted unusual movements in the trading of shares.

The board of directors of the Company confirms that the Company does not have any disclosable matters which remain undisclosed pursuant to related regulations of the Rules Governing the Listing of Stocks on the Shanghai Stock Exchange or any planning, negotiation, intention and agreement, etc., relating to such matters, nor is the board of directors aware of any disclosable information which remains undisclosed pursuant to related regulations of the Rules Governing the Listing of Stocks on the Shanghai Stock Exchange and may have a relatively material impact on the trading prices of the A shares of the Company and their derivatives. There is no clarification nor supplement to any information disclosed by the Company previously.

The deviation value of the increase in the closing prices of the A Shares of the Company accumulating more than 20% in three consecutive trading days constituted unusual movements in the trading of shares. The Company hereby seriously reminds the investors that only the information published on the website of the Shanghai Stock Exchange (www.sse.com.cn), the website of the Hong Kong Stock Exchange (www.hkexnews.hk) and other media as designated by the Company shall prevail. Investors are advised to beware of investment risks and make reasonable investment decision accordingly.

As at the date of this announcement, the directors of the Company are:

Beijing, the PRC

24 August 2021