The effecf of potassium fertilizer on Nitrate Reductase Activity (NRA), Hydrogen Peroxide Activity rn(HPA) ,Peroxidase Activity (PODA) in the fiber flax was studied on campus of NEAU in 1995 and 1996. The rnresult showed that the changing of NRA,HPA and PODA was same in the period from the quick growth to rnblossom period in the different treamets. NAR and HPA was the highest in the quick growth period then cut rndown gradually,and PODA was just right contrary. The other side,it was obviously different to NRA, HPA rnand PODA in the different Potassium levels. NRA and HPA presented the highest enzyme activity in the trearnment of K2O 22.5kg · ha-1. PODA in creased gradually with the increase of Potassium. PODA was the highrnest in the treament of K2O 67.5kg · ha-1. But all of the Potassium treatments was higher than CK whatever rnNRA,HPA and PODA. Potassium may enhanced the primary stem yield and fiber percentage and lead to fiber rnyield rising.