The invention discloses a nano-hydroxyapatite polycaprolactone nano-crystal composite fiber and a preparation method thereof. The composite fiber is prepared from polycaprolactone, nano-hydroxyapatiteand dispersant. The preparation method is as follows: polycaprolactone is dissolved into organic solvent, nano-hydroxyapatite and dispersant are then added, and thereby a mixed solution is obtained;after being refrigerated, the mixed solution is dried, so that a dry composite material sample is obtained; the composite material sample is cut into pieces, the composite material sample is put intoa vacuum oven and dried, the composite material sample is then put into a double-screw extruder, melted and extruded out, so that an as-formed fiber is obtained, and after being blown to be cooled, the as-formed fiber is wound by a winder; and finally, the as-formed fiber undergoes two-section drafting. The nano-hydroxyapatite/polycaprolactone nano-crystal composite fiber prepared by the inventionhas higher mechanical strength, and hydroxyapatite ensures that the fiber has good bioactivity, so that the fiber can become a candidate material in fields such as dentistry and orthopedics. The process disclosed by the invention is simple, environment pollution is little, and the production cost is low.