I hope you had a pleasant trip.

[jenny,Mei]

I meet one of my friends at a railway station, she just sees her friends off and I tell her that I am going to a resort for a holiday. when we say goodbye to each other, she says to me, 'I do hope you had a pleasant trip'

I don't know why we use 'had' in the sentence? why we don't use 'have' or 'will have'

[Harry Smith]

I meet one of my friends at a railway station, she just sees her friends off and I tell her that I am going to a resort for a holiday. when we say goodbye to each other, she says to me, 'I do hope you had a pleasant trip'

I don't know why we use 'had' in the sentence? why we don't use 'have' or 'will have'

It is a wish. I wish you had a pleasant trip. Of course she could say " Have a pleasant trip or Do have a pleasant trip.

[Philly]

I would not use 'had' the way you described.
'Had' would be appropriate after the trip is finished.

[Harry Smith]

I would not use 'had' the way you described.
'Had' would be appropriate after the trip is finished.

After the trip is finished we'd use "I hope you had had a pleasant trip."
e.g. I wish I had a nice at the party. And after the party someone can ask me, " I wish you had had a nice time at the party."

[Philly]

Hi Harry

If you already know that someone had an unpleasant trip, then and only then could you say "I wish you had had a pleasant trip." This is the sort of wish that refers to something unreal, impossible or in opposition to known fact.

This is something totally different from what Jenny, Mei described in her post.

[Harry Smith]

Hi Harry

If you already know that someone had an unpleasant trip, then and only then could you say "I wish you had had a pleasant trip." This is the sort of wish that refers to something unreal, impossible or in opposition to known fact.

This is something totally different from what Jenny, Mei described in her post.

O.k. I just meant that unreal wish saying that. Maybe better to say " I hope you could have a pleasant journey" or "I hope you to have a pleasant journey".

[Philly]

This write-up about "hope and wish" may help clarify things here.
.

I meet one of my friends at a railway station, she just sees her friends off and I tell her that I am going to a resort for a holiday. when we say goodbye to each other, she says to me, 'I do hope you had a pleasant trip'
I don't know why we use 'had' in the sentence? why we don't use 'have' or 'will have'

Jenny, Mei, if your holiday at a resort is not in the past, then you should not use had.
Both have and will have are correct in the context you described. Your feeling is correct here.
.

[jenny,Mei]

Thank Philly, and anyway,thank Harry Smith,too. You are so kind. Now I know that I was right, and I'll correct my friend.