Summer Holiday

During the first day, with my friend Arabella and I went to the Pudong airport to joined our Chinese tour guide and other members of our package tour.
Capitalization: always capitalize the first letter of a sentence.

Most nouns need an article preceding it. Since you are specifically talking about what you did during your first day there, you need to write "the first day".

When talking about multiple people, we first write the names/pronouns of other people, then ourselves. For example "my sister and I" - thus, "my friend Arabella and I"

All nationalities have to be capitalized.

There are were 16 members in our package tour.This was a small group.
Since you are describing something that happened in the past, you have to use the second person singular past of 'be', which is 'were'.

we are taking 5 hours by plane. After after a five hour flight, when we arrived at the Suvarnahumi International Airport , the local tour guide was waiting for us in there.
I've rephrased some parts of these sentences to make it sound more like fluent English. When there are people to wait on, we say we "wait for" them.

My first impression of Bangkok was like how China looked in the '90's.
After the phrase "first impression", we normally fully compare it to something, or associate it with a feeling. I think you meant to compare it to what China looked like, so that's how I corrected it.

Hope this helps! Let me know if you have any other questions! (:

Summer Holiday

When we got to Suvarnahumi International Airport, the local tour guide was waiting for us in there. My first impression of Bangkok is like China in the 90s.

寫得很不錯！

每一句話的頭一個字要大寫才對。

Chinese是proper noun，要大寫。

在逗號和句號前面不要加個空格。

注意時態。

Summer Holiday

At the end of every sentence with a comma or exclamation point, always capitalize the first letter once you begin a new sentence. Also capitalize a person, place or specific thing. When you are arriving at a place there is no need to repeat "there" because the place is already mentioned.