A field trial was carried out in two years in order to investigate the effect of potassium fertilizer on N,P2O5 and K2O absorption of alfalfa.The result showed that basic potassium fertilizer application decreased N and P2O5 content of first-year alfalfa,and increased K2O content.Shape curve was used to simulate N,P2O5 and K2O accumulation in alfalfa.Low potassium fertilizer application increased N and P2O5 accumulation,while high potassium fertilizer application decreased N and P2O5 accumulation.Potassium fertilizer application increased K2O accumulation,but K2O accumulation didn't continuously increase with potassium fertilizer increment.Potassium fertilizer had no effect on N absorption rate but could improve K2O absorption rate.Low potassium fertilizer application increased P2O5 absorption rate,high potassium fertilizer decreased P2O5 absorption rate.