Good letter, Calli.

A few quick suggestions:

1. re "Hello. How are you? This is WAN Yuti". This is typical of a face-to-face opening or telephone greeting. It is too conversational for a business letter. You could begin with "As discussed", as you have had prior discussions with this correspondent, and then launch right into your second paragraph, thus:

"As discussed, I am attaching a simple introduction ...."

2. Instead of "Please have a brief idea", I suggest "Please give it some thought" or simply "Please consider".

3. Instead of "We would like to hear advices on that", I suggest "We would welcome your suggestions on that".

4. Instead of "At the above link the publicized version of the recruitment information for the aforesaid item can be found", say "You will find our domestic marketing piece for this program at the link above". ["marketing piece" or "marketing brochure", either one, according to your own preference]

5. Instead of "You can find a third item about HSK", say "You will find ... ".

That's it. You should be proud of yourself, Calli. Your letter is very good.

One general suggestion which will always serve you well:

Always look for opportunities to say what you need to say with the fewest words possible.

Less is always more, particularly in a business letter.

And, whenever you can, break up long paragraphs into two or more paragraphs. The more white space you have in your letter, the easier and more inviting it will be to read.

You are almost at the point where you don't need anyone's help composing your letters, Calli. Congratulations!