The bombing in Helmand province is the latest by militants bent on weakening the Afghan security forces ahead of the withdrawal of most foreign troops at the end of this year.
The unidentified attacker approached the police compound in Lashkar Gah, the provincial capital, wearing a police uniform but was stopped by a guard at the entrance, said Farid Ahmad Obaidi, a spokesman for the Helmand provincial police chief.
The bomber detonated his suicide vest, killing one nearby police officer and wounding three other police and an army soldier, he said.