The invention discloses a pretreatment processing method of short flax fibers. The pretreatment processing method comprises the following steps: with the short flax fibers as a raw material, carrying out procedures of peracetic acid pretreatment, warm washing, sodium percarbonate-peracetic acid scouring, hot washing, cold washing, dehydration and drying. The pretreatment processing method has the beneficial effects that most impurities such as pectin and lignin in the short flax fibers are removed by virtue of an ecological environment-friendly aid, so that wastewater pollution is avoided; processing conditions are relatively mild, so that the problem that the fiber strength is greatly damaged due to strong base and high temperature in a traditional process is remedied; the procedures of scouring and bleaching are simultaneously finished, so that impurity removal and bleaching are finished, the processing process is shortened, and the production efficiency is improved; original auxiliary projects and facilities can be utilized, so that the operation is easy, and the cost is low; the processed short fibers are pure white, soft, high in splitting degree and good in spinnability, so that the quality of finished yarns is beneficially improved, the technical requirements of the production of flax yarns for circular machine weft knitted single jersey are well met, and the grade of application range is promoted.