The cathedral was destroyed in the raid on the night of January 2nd 1941.
The bomb tore off the Cathedral's roof and caused extensive damage in what turned out to be the most severe attack on any UK Cathedral, with the exception of Coventry.
No one of the actual site of the cathedral was killed as the Dean and the head verger, who had been on fire duty inside it at the time, managed to escape.
Dr John R Kenyon, from the Cardiff Archaeological Society told Premier that: "One parachute mine got tangled in the spire of the cathedral and then wrenched itself away and landed in the graveyard on the southside.
"It brought down most of the roof on that side of the cathedral."
"The Dean and the Verger were in the cathedral at that time, sort of late evening, but they escaped unhurt.
"Sort of shocked, and obviously a bit nervous, but they weren't killed or wounded in the bombing raid."
Elsewhere in the city that night the blitz killed 165 people and a further 427 were wounded.
Around 350 homes were also destroyed in the bombing raid.
On Sunday a special prayer vigil as well as thanksgiving and reconciliation service is being held to mark the anniversary.
After the raid, Llandaff Cathedral underwent a major restoration programme under instruction of the architect George Pace.
It was then another 17 years before the whole building was back in use.
Later a memorial chapel to the Welch Regiment was constructed and Sir Jacob Epstein was commissioned to create the figure of Christ in Majesty, which is suspended above the nave on a concrete arch.
It is now one of the defining sights of the Cathedral.
The Queen attended a service celebrating the completion of the restoration in 1960.
The area where the bomb fell, just outside in the grounds of the Cathedral, is now a garden of remembrance for those who have died.
The Dean of Llandaff, Gerwyn Capon, said: "This vigil will be a chance for us to remember that awful night in Cardiff when so many people lost their lives and their homes and our Cathedral was terribly damaged.
"It will also be a service of reconciliation when we pray for peace and an end to all conflicts.
"In the years that followed the Cathedral was restored and enhanced so that today we are blessed with a beautiful building that is a tremendous asset for the whole of the city."
Listen to Premier's Antony Bushfield speak to Dr John R Kenyon here: