The grave in Woodingdean Lawn Memorial Park was desecrated as a nearby plot was dug up.
The spoilt memorial was that of father Steven Kedian, who died aged 53.
His shocked relatives spoke of their anger at the damage, which happened on Friday and, they say, also affected other graves.
Son James Kedian, 24, said: “We were absolutely disgusted to find his grave in a shocking condition.
“All the little plants around the outside had been ripped out of the ground, the grave had sunk where their tractor had driven over it and the name plaque has been snapped in half.
“We take a lot of pride in painting our father’s grave and we are devastated that it has been left in this mess.”