The invention relates to a functional additive for strach- based biological degradation packing material and the preparation method. It belongs to a multi- functional premixer for adjuvant, and solves bad product performance caused from improper utilization of adjuvant agent. The components comprised by said fuctional additive and their weight proportion are as follows: demoulding agent 1- 10%, viscosity adjustment agent 10- 40%, plasticizing agent 5- 30%, fillings 20- 50%, crosslinking agent 1-5%, starch modifier 1- 5%. The process comprises following steps: feeding raw material into high- speed agitator, mixing for 10 minutes at 40 -80 Deg. C, discharging and getting functional additive. The additive is characterized in that it can greatly reduce fiber distribution speed, can improve slurry processing flowing property, is favouable for starch products shaping, can increase product flexibility and strength, meets non- degradation packing material property standard and state environmental requirment.