The invention provides a production method of flax / cotton blended yarns, which comprises the following steps of: 1, carrying out flax fiber pre-processing, i.e., firstly, carrying out flax rolling processing and flax carding processing on flax fibers, then spraying a softener to carry out softening, then sealing for 24h to enable the fibers to be softened, and packaging to obtain performance-improved flax fibers; 2, after mixing the flax fibers and cotton fibers, by sequential machining thorugh a disk plucker, a cotton blender machine, a porcupine opener, a multimixer, a card wire roller cotton slitting machine, a vibrating cotton feeding machine, a single beater scutcher, a carding machine, a three-pass drawing frame, a roving frame, a siro spinning frame and a winding machine, obtaining the flax / cotton blended yarns. According to the method provided by the invention, the produced flax / cotton blended yarns have the advantages of yarn evenness, small single yarn strength CV value, high strength and the like, can meet function requirements of consumers for a fabric, and have excellent development prospect.