The first bomber, who was on foot, detonated his explosive vest near the main gate of the Frontier Corps training centre at Shabqadar, 35 km from Khyber-Pakhtunkhwa capital Peshawar.
A large number of recruits who had completed their training were leaving for home at the time of the blast.
The second bomber, who was on a motorcycle, struck about eight minutes later as security personnel were removing the dead and injured from the spot.
A total of 73 people, a majority of them Frontier Constabulary personnel, were killed, a police official was quoted as saying by state-run PTV.
Over 100 injured people were taken to hospitals in Shabqadar and Peshawar, officials said.
Police officials said they feared the death toll could rise. The condition of 20 injured was described by officials as serious.
The recruits had recently completed their year-long training and passed out during a parade held on May 5, officials said.
They were going home on leave when the bombers struck. No group claimed responsibility for the attack. Such suicide bombings are usually blamed on the banned Tehrik-e-Taliban Pakistan.
This was the first major terrorist attack in Pakistan since US special forces killed al-Qaeda leader Osama bin Laden in a raid on a compound in the garrison city of Abbottabad, also in Khyber-Pakhtunkhwa province.
The Taliban and other militant groups had vowed to avenge bin Laden's death.