The invention relates to a process, and equipment for manufacturing cementitious material by using inert materials, which belong to the field of building materials. The raw material treating process comprises the following two parts that (1) an inert silicon-aluminum material and an alteration agent are formed into an alteration material with potential cementitious activity after passing through a hydrothermal alteration system and a pulverizing system, and the alteration material is fed into a midbin; and (2) a material with potential cementitious activity, a diagenesis agent and gypsum are fed into the midbin after directly passing through the pulverizing system, and then semifinished products inside the midbin are proportioned and stirred uniformly to form a cementitious material product. A hydrothermal alteration treating process is combined with a traditional pulverizing process through a steady flow bin and an alteration material bin, thereby ensuring that the hydrothermal alteration treating process and a traditional cementitious material pulverizing process become independent systems. The hydrothermal alteration treating system consists of a fluidized bed roaster, a drying machine and auxiliary equipment, wherein the drying machine is an internal heating type rotary kiln; and the front half part of the drying machine is a hydrothermal alteration reaction area, while the back half part is an alteration material cooling area. A cementitious material gelling material prepared by the process and the equipment has the advantages of low cost, ideal performance, energy saving, consumption reduction and environmental protection.