The preparation, mechanism and electromagnetic absorbing properties of Hollow Ceramic Micro-spheres (HCMs) were studied in the present investigation. HCMs were produced by traditional flame spraying technology as well as equipments. Al-TiO2 was chosen as a main reactive system. The self-reactive agglomerate powders were produced by spraying process by adopting a temperature-controlled media to get the high cooling rate to solidify and crystallize rapidly. HCMs with characteristic of hollow structure and in-situ synthesis were obtained. Electromagnetic parameter of HCMs has been tested and the reflectivity was analyzed. The results showed that HCMs possess the microwave absorbing properties. The relationship between intrinsic parameters of HCMs and microwave absorbing properties has been also investigated.