Alite in industrial clinker is usually M3 type as the presence of MgO.It is also reported that the M3 type of alite performs not as good as the M1 type.A promised 10% increment of the strength by the modification of M3 to M1 was reported.SO3 can modify alite polymorph in the MgO contained clinker.In this paper, the modification of alite by SO3 was performed in an industrial production line with the production of 2000 t per day.The mineral composition of the clinker and the formation of clinker were investigated.The modification of the alite polymorph on industrial line was made by addition of desulfurized gypsum into the raw meal.1.15~1.39% of SO3 in the clinker could yield M 1 alite for clinker with ~2.66% MgO.Within the gypsum amount added, clinker can be produced, but more attention should be paid to maintain a steady production of the clinker.Alite content decreased as the existence of extra SO3 in the clinker, which complicated the relationship between the alite polymorph and the compressive strength.All the mechanical properties fall in the demand of the standard.