Because　of　the　special　needs　for　nanosecond　double　pulse　applications　in　micromachining　and　material　processing,　we　demonstrated　a　stable　nanosecond　dual-pulse　erbium-doped　fiber　laser　based　on　nonlinear　polarization　rotation　technology.　The　fiber　laser　operates　in　a　normal　dispersion　regime　with　a　length　of　256　m　OFS-980　fiber.　With　the　pump　power　of　1120　mW,　the　laser　generates　a　highly　stable　dual-pulse　train　with　the　pulse　widths　of　6.2　ns　and　1.2　ns　respectively.　By　simply　changing　the　pump　power,　the　pulse　width　of　one　of　dual-pulse　can　be　tuned　from　2.1　to　6.2　ns　while　the　other　pulse　keeping　almost　the　same　duration　of　1.2　ns.　The　maximum　dual-pulse　energy　is　about　72.5　nJ　with　a　repetition　rate　of　783.3　kHz.　The　formation　of　such　nanosecond　dual-pulse　is　attributed　to　the　pulse　splitting　and　depends　on　the　parameters　of　the　laser　cavity,　such　as　the　cavity-length　and　the　state　of　polarization　controller.　The　experiment　of　a　single　square　pulse　splitting　into　different　shapes　of　nanosecond　dual-pulse　was　demonstrated.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.