The invention discloses a carbon fiber gas cylinder detection line and a carbon fiber gas cylinder detection method. The detection line includes, in a front-to-back arrangement manner, a water pressure test apparatus, a water pressure auxiliary test apparatus and an air tightness test apparatus. The water pressure test apparatus includes a test rack, a test operation bench, a pressurizing apparatus, a test case installed on the test rack, and test trolleys for stably placing a plurality of to-be-tested gas cylinders. The water pressure auxiliary test apparatus includes a gas cylinder fixture, a transporting trolley, and a gas cylinder water-pouring-away and drying device. The air tightness test apparatus includes an air tightness detection apparatus and a second air supply apparatus for supplying air to the to-be-tested gas cylinders. The air tightness test apparatus is in a cabinet structure or a ground trough structure. The detection method includes the steps of 1) water pressure test; 2) water pouring-away and drying treatment; and 3) air tightness test. The detection line is reasonable in design and simple in operations, is good in use effects, and can easily and quickly complete water pressure test and air tightness test for a plurality of carbon fiber gas cylinders.