Motor　structure　was　improved　for　increasing　its　efficiency　and　the　impact　of　these　measurements　to　motor　operating　characteristics　was　analyzed.　It　is　shown　that　increasing　wire　diameter　can　reduce　stator　copper　loss　and　increase　efficiency　effectively　within　a　limited　fill　factor.　Reducing　gap　thickness　can　increase　motor　efficiency　and　power　factor　but　will　increase　locked-rotor　current　ratio.　Increasing　iron　core　length　properly　can　raise　motor　efficiency　and　power　factor,　but　it　will　reduce　locked-rotor　torque　ratio　and　breakdown　torque　ratio.　Using　cast　copper　instead　of　cast　aluminum　as　rotor　bars　and　end　rings　can　increase　efficiency　but　will　reduce　locked-rotor　torque　ratio　and　raise　locked-rotor　current　ratio　at　the　same　time.　©　2011　IEEE.