The integral impeller with uniform-section blade is widely used in engines of aerospace and weaponry. The electrochemical trepanning machining has obvious advantages in decreasing the machining cost and improving the machining efficiency of uniform-section blade. In order to solve the stability problem in the electrochemical trepanning machining process of narrow channel integral impeller, the composite cathode and tooling fixtures with closed flow field were designed innovatively, and the electrochemical machining verification test was carried out. The results show that the composite cathode can effectively solve the instability problem caused by the large difference between the vane spacing of the blade tip circle and the blade root circle. The closed flow field improves the distribution uniformity of electrolyte pressure and electrolyte velocity in the machining region. The surface quality of blade is high, and the machining process is stable, which lays a technical foundation for the high quality and efficient processing of the narrow channel integral impeller.