Electrochemical machining (ECM) is suitable for machining parts with complex cavities and made by material that hard to cut. However, allowance distribution of complex cavities during ECM still needs to be researched further. To solve the problems that angles between normal direction and feeding direction are different at points on cathode surface, making forming process changed, differential equations of machining gap at points with specific angles were constructed to simulate different angles between normal direction and feeding direction. Cathodes with regular shapes were used to carry out contrastive experiments of direct current ECM and pulse-vibration ECM to choose suitable differential equations to simulate forming process of complex cavity under the above machining  modes. Achievement of research has been used in efficient machining of integral shrouded blisk channels.