Hi Jian!
What better way to celebrate the day after Thanksgiving than a journey to the "Wonderful World of Disney!"
I should note, however, that Mickey's Very Merry Christmas party is not scheduled on the 26th. If you'll be at Disney around that time, then the next scheduled Mickey Party is Sunday, November 28th.
But, to answer your question, to attend Mickey's Very Merry Christmas Party, you must have a separate ticket even if you already have regular Park admission tickets for the day. There are a number of special events and experiences during the Party, and cast members will be checking to see if attendees have Party wristbands to remain in the park.
So, if you're staying for a few days and wish to experience The Party, I'd contact Disney right away at 407-934-7639 to reserve a spot!
Have a fantastic holiday season!