This paper deals with the stator cooling structure of yokeless and segmented armature (YASA) axial flux machine. An innovative direct water-cooling system is presented to enhance the heat transfer performance of the YASA stator. Three types of water channel structures are compared to verify their thermal performance by computational fluid dynamics (CFD) simulation. The results show that the proposed stator cooling system can improve the temperature of the stator significantly, and the water channel Structure C of three structures can achieve the best cooling performance.