[Objective] The IE5 energy efficiency class is currently the highest global standard for low-voltage three-phase asynchronous motors, corresponding to the 1st energy efficiency level in the national standard GB/T 18613—2020. In response to the lack of unified design for IE5 energy efficiency series motors in China, the Shanghai Electrical Apparatus Research Institute has organized the development of the YE5 series (IP55) three-phase asynchronous motor to promote the advancement of 1st energy efficiency motors. The IE5 energy efficiency is the highest global standard, equivalent to the 1st energy efficiency level in GB/T 18613—2020. [Methods] A working group was formed by uniting leading manufacturers and upstream/downstream enterprises. Based on the joint design of IE2 efficiency motors, energy-saving technologies such as unequal-slot design, stamped air-gap process, and low-pressure aluminum die-casting were comprehensively applied, significantly reducing additional motor losses and thereby improving motor efficiency. [Results] The complete product series of low-voltage three-phase asynchronous motors was developed through breakthroughs and applications of key technologies. Prototype testing of 30 units across 16 specifications demonstrated that all motor efficiencies met the IE5 efficiency limits specified in GB/T 18613—2020, confirming the design’s validity. [Conclusion] This project achieves the first unified industry design for a series of 1st energy efficiency low-voltage three-phase asynchronous motors in China, filling a product gap and providing crucial practical support for the energy efficiency upgrade of the motor industry.