The integral impeller made of difficult to machine materials is widely used in the aviation field. The traditional machining has the problems of fast tool wear and low machining efficiency. In this paper, a large cutting depth five axis numerical control electrochemical milling pre-processing method is proposed for a certain type of complex integral impeller. Through the design of the conical spiral blade cathode, the flow field distribution at the outlet of single and double spiral blades with different rotation angles is analyzed, and the distribution of the pressure and flow velocity at the outlet of the single spiral blade cathode with rotation angle of 720° is uniform. At the same time, the experiment of NC electrochemical milling with large cutting depth is carried out. The results show that: Within the range of selected process parameters, the machining balance gap and feed speed increase with the increase of machining voltage; The lower electrolyte temperature is conducive to the realization of small gap machining, which can significantly improve the machining accuracy; The spindle speed reaches 1 500 r/min, which has little impact on the machining speed. The results show that the maximum cutting depth can reach 65 mm, and the margin error can be controlled within 0.5 mm, which improves the machining efficiency of the whole impeller.