Abstract: For lack of research of nonlinear and linear solution algorithms of selected harmonics elimination pulse width modulation used in the same level topology of inverter, a nonlinear solution equation based on homotopy algorithm and a linear solution model based on Walsh function were established for a cascade multilevel inverter. Under several topology conditions, trajectory, upper limit and harmonic elimination effect of switching angles solved by the two algorithms were compared, and setting of initial solution conditions of the two algorithms were analyzed based on multi-band modulation mode. Solving characteristics, advantages, disadvantages and applicability under different control conditions of homotopy algorithm and Walsh function were summarized. It was pointed out that applying the two algorithms in the same level topology of inverter could reduce solution amount and improve control flexibility.