Abstract: The present invention relates to carbon nanotube fiber and a producing method thereof. The carbon nanotube fiber has a tensile strength which exceeds 5 GPa, and the producing method includes: producing a carbon nanotube fiber precursor consisting of carbon nanotubes; evenly dispersing a cross-linking agent on the carbon nanotube fiber precursor; and acquiring carbon nanotube fiber by thermally treating the carbon nanotube fiber precursor wherein the cross-linking agent is evenly dispersed, wherein the acquired carbon nanotube fiber has cross-linking between wall surfaces of the carbon nanotubes each other.