In this contribution, we present the preparation of high purity niobium ingot for RF superconducting cavities by more than three times electron beam melting under high vacuum. The purity of obtained high pure niobium ingots were more than 99.99%, and RRR value reached more than 300. High pure niobium ingots has reaches the standard specifications for RF superconducting cavities.The RRR value of high purity niobium ingot is mainly affected by the interstitial impurities such as H、N、O、C, while the standard of Ta content can be relaxed moderately. With increasing the number of electron beam melting, the interstitial impurities can be removed effectively, and RRR values grow steadily.The results show that, RRR value and impurity content should be combined to evaluate the quality of high purity niobium, while impurity content alone is insufficient.