<p>Electrolyte jet machining (EJM) offers promising post-processing capabilities for such AM parts, owing to its advantages of no tool wear, absence of cracks and heat-affected zones, no residual stresses, and insensitivity to material hardness. This work presents an in-depth theoretical study on the flattening of uneven surfaces using EJM. A mathematical model for EJM on stepped surfaces is proposed, and theoretical formulas for calculating the flatness of stepped surfaces under both single-path and multi-path machining are derived. Numerical analyses under different process parameters are performed, and the results are compared with the theoretical predictions. Results show that the deviation between the theoretical and numerical data on an uneven surface is within 12%, with a minimum of 2.19%, indicating a high degree of consistency between the theoretical model and numerical simulation. Finally, the theoretical predictions are verified using previously reported experimental data. The deviations between the theoretical predictions and experimental data are within 15%, with a minimum of 4.77%, showing a good prediction accuracy. The findings provide theoretical guidance for selecting process parameters in the post-processing of AM parts using EJM.</p>