The skin effect and proximity effect at high frequencies would greatly increase the AC copper loss of high speed permanent magnet machines (HSPMMs), especially for form-wound windings. However, the influence of some factors on the AC loss of the form-wound winding is still unclear in the existing research. Therefore, this paper presents comprehensive research on the AC copper loss of HSPMM with form-wound windings. Firstly, the model of eddy current field considering the skin effect and the proximity effect for form-wound windings is established, and the AC losses of each stator slot and each conductor at high frequency are obtained. In addition, the factors affecting the AC loss are comprehensively analyzed through the eddy current field, including the conductor size, the number of conductors per slot, and the operating temperature. Furthermore, the influence of strand wire sizes on temperature distribution of HSPMM is also implemented by establishing a temperature calculation model. Finally, the theoretical results are verified by testing the AC resistances of five coils at different frequencies and the temperature characteristic of an HSPMM prototype with form-wound windings.