A design method of a transformer, wherein the transformer comprises at least one secondary winding set, each secondary winding set comprises a plurality of secondary windings (11, 12, 13, 14); and the method comprises: repeating following steps until a preset condition is met: calculating an output voltage of each secondary winding (11, 12, 13, 14) according to a phase shift angle and a number of turns of the each secondary winding (11, 12, 13, 14); obtaining a difference between output voltages of each secondary winding pair in a secondary winding set; adjusting the phase shift angle of at least one secondary winding (11, 12, 13, 14) in the secondary winding set; and obtaining a final number of turns for the each secondary winding (11, 12, 13, 14) according to a resultant phase shift angle corresponding to when the preset condition is met, wherein the preset condition is that the difference between the output voltages of any secondary winding pair in the secondary winding set is less than or equal to a preset threshold, wherein the adjusting the phase shift angle of at least one secondary winding (11, 12, 13, 14) in the secondary winding set comprises: adjusting a phase shift angle of an i-th secondary winding (11, 12, 13, 14) in the secondary winding set according to a first preset incremental angle; and, adjusting a phase shift angle of an (i+1)-th secondary winding (11, 12, 13, 14) in the secondary winding set according to the first preset incremental angle if the phase shift angle of the i-th secondary winding (11, 12, 13, 14) has been adjusted according to the first preset incremental angle by more than a preset number of times but the preset condition is still not met; wherein i is greater than or equal to 1. repeating following steps until a preset condition is met: calculating an output voltage of each secondary winding (11, 12, 13, 14) according to a phase shift angle and a number of turns of the each secondary winding (11, 12, 13, 14); obtaining a difference between output voltages of each secondary winding pair in a secondary winding set; adjusting the phase shift angle of at least one secondary winding (11, 12, 13, 14) in the secondary winding set; and obtaining a final number of turns for the each secondary winding (11, 12, 13, 14) according to a resultant phase shift angle corresponding to when the preset condition is met, calculating an output voltage of each secondary winding (11, 12, 13, 14) according to a phase shift angle and a number of turns of the each secondary winding (11, 12, 13, 14); obtaining a difference between output voltages of each secondary winding pair in a secondary winding set; adjusting the phase shift angle of at least one secondary winding (11, 12, 13, 14) in the secondary winding set; and obtaining a final number of turns for the each secondary winding (11, 12, 13, 14) according to a resultant phase shift angle corresponding to when the preset condition is met, wherein the preset condition is that the difference between the output voltages of any secondary winding pair in the secondary winding set is less than or equal to a preset threshold, wherein the adjusting the phase shift angle of at least one secondary winding (11, 12, 13, 14) in the secondary winding set comprises: adjusting a phase shift angle of an i-th secondary winding (11, 12, 13, 14) in the secondary winding set according to a first preset incremental angle; and, adjusting a phase shift angle of an (i+1)-th secondary winding (11, 12, 13, 14) in the secondary winding set according to the first preset incremental angle if the phase shift angle of the i-th secondary winding (11, 12, 13, 14) has been adjusted according to the first preset incremental angle by more than a preset number of times but the preset condition is still not met; wherein i is greater than or equal to 1. adjusting a phase shift angle of an i-th secondary winding (11, 12, 13, 14) in the secondary winding set according to a first preset incremental angle; and, adjusting a phase shift angle of an (i+1)-th secondary winding (11, 12, 13, 14) in the secondary winding set according to the first preset incremental angle if the phase shift angle of the i-th secondary winding (11, 12, 13, 14) has been adjusted according to the first preset incremental angle by more than a preset number of times but the preset condition is still not met; wherein i is greater than or equal to 1.