16 January 2017 Last updated at 12:32 GMT
The ceremony is called the inauguration.
At the event, he will make a promise to do the best for the country and will give a speech known as the inaugural address.
There are a few traditions passed down, which he must observe on his inauguration day.
Leah takes a look at what's going to happen throughout the day...

Staffordshire County Council has a 99-year-lease on the Shugborough Estate in Stafford until 2065.
But now it wants the National Trust, which owns the Grade I-listed site, to take it back off its hands.
A spokesman for the National Trust has said it is exploring options for the management of the estate.
Mark Winnington, Staffordshire County Council's cabinet member for economy, environment and transport, said: "We are meeting colleagues at the National Trust to explore the feasibility of relinquishing our lease and passing the management of the Shugborough Estate to them."
The council said it expected to spend Â£650,000 this year maintaining and running the Shugborough Estate.
A spokesman said it took the lease on at a time when the National Trust was not as large. He said there was no threat to the building and the council would continue to manage it if an agreement could not be reached.
National Trust regional director Harry Bowell said: "At this stage the National Trust is working in partnership with Staffordshire County Council to carry out early-stage feasibility studies to explore options for the management of the Shugborough Estate.
"It is important to stress that no decisions have been made at this stage."
Shugborough was one of the manors of the bishops of Lichfield in the Middle Ages. The site was purchased in 1624 by William Anson, a lawyer. The current house dates back to 1694.

Tobefair, a seven-year-old gelding, has won his last seven races.
He was gifted as a colt to Michael Cole three years ago, in return for looking after two fillies on his farm.
Unable to afford the training costs on his own, he decided to offer 50% of the ownership to people he knew through his local pub, the Cresselly Arms at Cresswell Quay.
The syndicate grew to 17 members but none except Mr Cole had owned a racehorse before.
They said they were amazed when Tobefair started winning races and never dreamed he would make it to Cheltenham.
The festival runs from Tuesday to Friday and culminates in the showpiece contest, the Gold Cup.
Mr Cole said: "There's a lot of these big people now, they've got 40, 50, 60 horses, and it doesn't mean anything. But it means something to us."
Syndicate member Andy Pannell described the experience as "total exhilaration", adding: "We were stood on the steps at Newbury and I thought I was going to have a heart attack. My heart was pounding, thumping."
This is also a first appearance at the Cheltenham Festival for Tobefair's trainers Debra and Paul Hamer's, whose yard is at Nantycaws near Carmarthen.
At least two bus loads of supporters will be travelling from the Cresselly Arms to Cheltenham for Tobefair's race, the Pertemps Final Handicap Hurdle, on Thursday.
But syndicate member Jennifer Cole said they have only one real wish: "Win or lose, just get him round the track and bring the boy home."
On Friday, Donald Trump will officially become the next president of the United States.
[NEXT_CONCEPT]
The National Trust could take back responsibility for a 17th Century estate to save a council hundreds of thousands of pounds a year.
[NEXT_CONCEPT]
A racehorse owned by a syndicate from Pembrokeshire is a favourite to win at this year's Cheltenham Festival.