Abstract: In order to study iron loss distribution characteristics in stator and rotor core of asynchronous motor,an iron loss computation model,with slot skew considered,was established based on time-stepping finite elements （T-S FEM）.Taking Y132S-4,5.5kW motor with traditional structure as an example,the time variation of flux density and loci of flux density at different core locations were firstly analyzed,then iron loss distributions in different areas in the core were concluded.It is shown in the paper that high loss density values appear in the areas at middle of the tooth top for both the stator and rotor.Further,loss distributions in different core areas were analyzed based on the computed loss density,it is found that,in stator side,iron losses mainly distributed at the boundary between teeth and yoke,in yoke,as well as in tooth bodies.The iron losses in those three areas are 32%,28% and 17.5% respectively,of the total calculated iron loss in the machine.Although the iron loss densities in the tooth top of the stator are high,however they only contribute a small percentage at 2.5% to the overall iron loss of the machine.Meanwhile,at rotor side,the iron loss in the tooth top area which is normally neglected in traditional analysis,contributes 15% to the overall iron loss of the machine.The iron loss in the rotor tooth area is clearly due to high harmonics.The achievement in this paper could provide necessary technical support for developing optimized design of core structure to reduce iron losses.