Ultra-wideband signals have the advantages of low power consumption and anti-attenuation in human body communication technology. Aiming at the problem of the correlation between shadow fading and motion state in the human body channel modeling work, this article establishes a human body model based on the human body's different motion postures and the electromagnetic characteristics of tissues, and analyzes the dynamic human body channel shadow fading characteristics under ultra-wideband signals. First, by establishing 80 data transmission links to analyze the body surface propagation characteristics of the human body in different states, a second-order exponential attenuation relationship between body surface propagation distance and path loss is given. Secondly, the influence of changes in the electrical characteristics of the dynamic model organization on the path loss is analyzed. Finally, the average bit error rate is used to study the performance difference of UWB system under dynamic shadow fading. The results show that the antiloss performance of the UWB frequency band under the dynamic human body model is better than that of the HBC frequency band, and the intensity of shadow fading is affected by the motion state more than the HBC frequency band. The research provides a theoretical basis for dynamic human shadow fading intensity distribution in the modeling and application of ultra-wideband signals in human body communication.