The Hen Harrier Action Plan, supported by a number of groups, was set up in January to help the "persecuted" birds.
However, the RSPB said "illegal killing" and "depressing" incidents, including one involving an armed man in the Peak District, have continued.
The government said the plan was still at an early stage and remains the best way to safeguard the birds in England.
The plan followed the disappearance of five male hen harriers in 2015, leading to the collapse of nests.
The birds' predation of grouse is a source of conflict on moors used for shooting, but there was hope the decline could be halted through a joint approach.
However, in April, a video emerged apparently showing an armed man using a decoy bird to attract a hen harrier in the Derbyshire Peak District.
This later led to the National Trust terminating a grouse shooting lease for the first time on its land.
In May, a man was caught on camera setting illegal pole traps on the Mossdale estate, in North Yorkshire, and later lost his job.
Martin Harper, the RSPB's conservation director, said these incidents were "depressingly predictable" and the charity has withdrawn its support as a result.
He said there have only been three nest attempts this year, none on moorland, and reform could only come from the "licensing" of driven grouse shooting.
Amanda Anderson, director of the Moorland Association, said she was "disappointed" by the decision and stressed there were elements of the plan yet to be investigated before the project could be judged a success or not.
She said: "We wish to reiterate our total abhorrence of any act of wildlife crime and support of prosecutions.
"The onus is on every estate to ensure every employee is working within the existing law. Nothing less will do."
A Department for Environment, Food and Rural Affairs (Defra) spokesman said it was committed to protecting hen harriers and would continue to work with its remaining partners.
*The RSPB said none of these have been on grouse moors.
A government plan to increase hen harrier numbers on England's moors has failed, the RSPB said.