The invention discloses a flax blended yarn and a preparation method thereof. The flax blended yarn comprises flax fibers and PTT fibers which are in the mass percentage of (60-95):(5-40), wherein the flax fibers are long flax fibers; the preparation process of the flax blended yarn comprises the following steps in sequence: strip forming, drawing, roving, boiling and bleaching, blending, yarn fault cutting. The wool type blended fabric obtained by the preparation process has good fabric performance, has the functions of regulating temperature, resisting allergy, preventing static electricity, preventing ultraviolet rays, and resisting bacteria, has bright and clean surface, stiffness, smoothness and breathability, strong woolen-type feeding and soft texture, is comfortable to wear due to excellent extendibility, is fluffy and rich in elasticity due to soft buffering capacity, shrinks or deforms slightly after being worn repeatedly or washed and dried repeatedly due to excellent side stability and shape reducibility, and can be dyed into different colors as required due to good color emissivity.