He arrived in Poland on Wednesday to celebrate the event, with millions from all over the world expected to attend.
However the atmosphere is likely to be one of sadness and reflection following Islamic State's murder of parish priest Fr Jacques Hamel in Normandy.
General view of the church where a priest was killed in an attack in Saint Etienne du Rouvray, Normandy, France, Tuesday, July 26th 2016.
On Tuesday two men with knives took several people hostage in a church in the town of Saint-Etienne-du-Rouvray. The men were killed by French police.
The pontiff is expected to pay tribute to the murdered priest.
Some are calling for Fr Jacques Hamel to be declared a martyr because of the way he was killed for his faith.
Speaking to Reuters ahead of the visit of Pope Francis, a pilgrim in their 20's called Guillaume said: "We listened to the news with disbelief, we got phone calls from our parents who tried to reassure us.
"Pope John Paul II said that we should be tolerant and not resort to force.
"My heart tells me that this is true, but after what happened my head is now telling me something else."
Security has been stepped up for World Youth Day and during the visit the Pope is expected to give nine speeches and three public homilies.
French police officers stand guard in front of the Saint-Etienne-du-Rouvray's city hall, Normandy, France, after an attack on a church that left a priest dead.
Speaking earlier in the week the Vatican said Pope Francis shared the "sorrow and horror" felt over the incident.
It released a statement that read: "We are particularly struck because this horrible violence has occurred in a church - a sacred place where we pronounce God's love - with the barbaric murder of a priest and worshippers affected."
The pope is also expected to speak about immigration in the nation that has not been praised for its closed border policy.
During his visit the pope is also expected to visit Nazi concentration camps at Auschwitz and Birkenau, as well as pray at the site of Poland's holiest shrine.
