The invention relates to a process for treating flax rough yarn. The prior sub-oxygen bleaching chemical degumming processes have complex flow, large water usage, large energy consumption, highly toxic substances in the chloride bleaching waste water and high pollution to environment. The process comprises the following reaction steps: step one, boiling-off and oxygen-bleaching, namely adding sodium hudroxide, hydrogen peroxide, sodium silicate, calcined soda, osmotic agent, carbonyl diamide, sodium tripolyphosphate and sodium sulfite into water, and heating and boiling off the mixture; step two, washing by water, namely washing the mixture once or twice by hot water and twice or thrice by cold water, and washing the mixture by overflow; step three, washing by acid, namely using acetic acid and adding the osmotic agent into the acetic acid; step four, washing by water, namely washing the mixture twice or thrice by cold water, and washing the mixture by overflow; and step five, soft treatment, namely adding alkyl silicon composite RS into the water. The process adopts the method of combining carbomite and the hydrogen peroxide to replace sodium chlorite which is a toxic bleaching agent, is favorable for environmental protection, improves whiteness of yarns at the same time, and reduce production cost.