The invention discloses a molten steel calcium treatment process adopting a pure calcium line, belonging to the technical field of steelmaking. The process technology realizes stable industrial application of the pure calcium line in calcium treatment through structural optimization of the pure calcium line and control on the technological parameters in a line feeding process, wherein in the structural optimization, a high-density solid pure calcium rod is adopted for an inner core, and the calcium content, cored wire diameter and steel belt thickness are guaranteed; the technological parameters include the molten steel oxidability, steel slag oxidability, line feeding speed and molten steel temperature. The process disclosed by the invention has the advantages that the problem of silicon increase in a line feeding process adopting the pure calcium line is solved, and the structural design of the pure calcium line guarantees enough line feeding depth; meanwhile, by adopting low-speed line feeding, the problem of splashing in the application process of the pure calcium line is solved, secondary oxidation of molten steel in the line feeding process is reduced, the yield of the calcium element is stably controlled above 25%, large-scale batch application is realized, and the smelting cost is lowered.