The invention discloses a process for preparing flame retarding cellulose viscose, which adopts pyrophosphate exchange reaction flame retardant particle whose mean particle diameter is <= 1.0um, non-ionic surface active agent, dispersing agent and solvent water to mix and obtain flame retardant emulsion, each percentage by weight is pyrophosphate exchange reaction flame retardant 20-45 wt%, non-ionic surface active agent 5-10 wt% and dispersing agent 0.5-1.0 wt%, and residue is solvent water. The process for preparation comprises adding pyrophosphate exchange reaction flame retardant of flame retardant emulsion which is corresponded to alpha cellulose 15-30 % into spinning original liquid which is filtered to mix, shaping spinning by adopting spinning bath which is low acid, low salt, low temperature and high zinc. The spinning original liquid of the invention has simple and convenient preparation, fiber does not contain halogen elements, which avoids environmental pollution, when in burning, the invention is not melted, while charring only happens to keep the original shape of fiber, the invention prevents dripping which is melted in high temperature from scalding human body, and flame retardant is distributed evenly in adhesive, which can not smolder after leaving fire and easy to be self-extinguished.