Hello Giang, are you referring to importing through the Sites module? If so, I would recommend moving the file over to the server via FTP if possible ( you would move it to '~\CMSSiteUtils\Import\' ), and then unzipping the import.zip file into a folder with the exact same name as the zip, for example:
I have the following import.zip file:
So I will extract this zip file to a directory with the same name, the folder will be called:
You know you have extracted it correctly if directly under that folder you see a Data folder.
The reason I recommend this is two reasons, first moving it to the server makes it so you don't have to upload it and wait for .NET to upload it correctly ( .NET is not very good at sending large files usually ). And Second, moving it into a folder instead of a ZIP file will cut down drastically on time since one of the first things the import usually has to do is unzip and this process can take a while if you don't already have it done. Try these suggestions and see how long it takes, it should be quite a bit shorter.