Kate and William are planning to personally deliver gifts to the military personnel and their families to make their Christmas extra special.
The Royal British Legion - who organise the UK-wide Poppy Appeal - is supporting the party.
Over the years, William and Kate have become known for their ability to put people at ease during public events.
Gareth Bradbury, who met the couple during their visit to Yorkshire, said:
“They are warming people. They have an almost calming vibe that puts you at ease.”