During the raids on 7-8 May and 8-9 May 1941 more than 400 people were killed in the East Yorkshire port.
In all 1,200 were killed, 3,000 injured and more than 150,000 were made homeless by German raids on the city.
A service has been held at Holy Trinity Church and a book about the attacks has been launched.
The book written by a local author, mixes fact and fiction with any profits going to the Hull People's Memorial fund.
Hull suffered numerous air raids because it was a port, easy to find, and German aircraft flew over it to reach other targets such as Sheffield, Liverpool or Manchester.
Alan Bingham, of the Hull People's Memorial, said: "I think it is extremely important to remember the people who lived through the blitz and who survived.
"They have lived through the nightmares for the rest of their lives. Some of the sights they have seen must have been truly horrendous."
Source: A North-East Coast Town - T Geraghty
The Rev Canon Dr Neal Barnes, Vicar of Holy Trinity Church, said: "The city was really traumatised and we wanted to help the people to remember."
The service in the church included  popular songs from WW2 to "get into the mood that helped Hull get through those dark days", he added.
Other events and exhibitions to mark the blitz are being held over the weekend.
The heaviest bombing raids on Hull during World War Two are being commemorated in a series of events in the city.