Closed blade ring is a type of integral component with superior weight reduction performance, however, it is difficult to machine due to its closed structure, poor openness, narrow and twisted channels, and limited tool feed space. Electrochemical machining (ECM) is a non-traditional machining method, which has the advantages of not being affected by material mechanical properties, no loss of tool cathode, and high machining efficiency. It is one of the important methods for machining closed blade rings. However, there is relatively little research on the flow field of closed blade ring slotting ECM, and the stability of the flow field requires to be improved. Thus, a forward flow liquid supply flow method was proposed for closed blade ring slotting ECM, and flow field simulation and optimization studies were conducted under 1 mm, 2 mm, and 3 mm outlet slot widths. The results show that: (1) The cathode with a slit width of 2 mm had better uniformity and accessibility of flow field in the gap. (2) After adjusting the position of the liquid gap and designing the drainage groove structure according to the principle of equal process, the local liquid shortage phenomenon at the edge of the blade has been effectively improved. Three experiments of closed blade ring slotting ECM were conducted under different liquid outlet slot widths. The results show that the cathode with optimized flow field structure can realize stable machining, and the relative feed speed between the tool cathode and the workpiece was increased from 0.79 mm/min to 0.98 mm/min. The surface quality of the channel was relatively optimal, the roughness of the convex surface decreased from 2.681 μm to 1.641 μm, the roughness of the concave surface decreased from 2.482 μm to 1.243 μm. This verifies the effectiveness of the flow method and the correctness of the flow field simulation results.