Preposition

It all depemds on how it is used in the context.

I think "the" is ok.



On the Mid Autumn Festival Day, it a Chinese tradition for families to celebrate with everyone in the family.



At the Mid Autumn Festival celebration, everyone had a cheerful time.

I disagree (if I understand the previous poster aright). Since you have capitalized 'Festival', I presume that it is actually part of the name of the holiday; hence, no article:

At Mid-Autumn Festival
At the mid-autumn festival

(Only 'at' in your original text, but 'on...day/Day' is OK.)

Sorry! Please educate me.

The way I understand it is:

The article pertains to the celebration and Mid Autumn Festival mermely described what celebration it is, and since it is a proper name, why shouldn't it be capitalized?

At the Mid Autumn Festival celebration, everyone had a cheerful time.

On the Mid Autumn Festival Day, it a Chinese tradition for families to celebrate with everyone in the family.
At the Mid Autumn Festival celebration, everyone had a cheerful time

There is nothing wrong with your second sentence, since 'the' refers to the common noun, 'celebration'. It is your first sentence that should omit the article, just as we omit it for

I got it. Thank you very much for your help.