The　effects　of　polyacrylonitrile　fiber　on　the　fatigue　strength　and　endurance　limit　of　concrete　structures　were　studied　using　the　third-point　loading　method　to　determine　the　fatigue　properties　of　polyacrylonitrile　fiber　reinforced　concrete　beams　with　and　without　bottom　layer　steel　fibers　to　design　economic　concrete　structures　with　excellent　properties.　The　test　results　show　that　with　a　polyacrylonitrile　fiber　volume　fraction　of　0.085%,　the　flexural　fatigue　strengths　of　polyacrylonitrile　fiber　reinforced　concrete　beam　with　and　without　bottom　layer　steel　fibers　were　larger　than　the　plain　concrete　beams　by　11.7%　and　15.7%,　respectively.　For　a　fatigue　stress　ratio　of　0.9,　the　fatigue　cycles　of　the　polyacrylonitrile　fiber　reinforced　concrete　beams　with　and　without　bottom　layer　steel　fibers　were　22　and　29.01　times　larger　than　that　of　the　plain　concrete　beams.　The　flexural　fatigue　strength　of　the　polyacrylonitrile　fiber　reinforced　concrete　beams　with　bottom　layer　steel　fibers　was　better　than　concrete　beams　with　only　bottom　layer　steel　fibers　or　only　concrete　reinforced　by　polyacrylonitrile　fiber.　The　polyacrylonitrile　fiber　reinforced　concrete　beam　with　bottom　layer　steel　fibers　is　an　ideal　structure　for　constructing　concrete　highway.