Abstract: This is a paper in the field of mineral materials. In order to seek for a new feasible way to utilize low-grade pyrite cinder under local conditions, to solve bottleneck problems of large reserves, and to relieve soil and water pollution, a research on the process optimization on preparation of composite portland cement with low-grade pyrite cinder was conducted. Pyrite cinder as a special kind of industrial solid waste with higher iron content, was used as additive, and was incorporated with portland cement clinker, flue gas desulfurization gypsum and fly ash to prepare composite portland cement. Their efficacy was compared by testing the compressive strength and flexural strength of composite portland cement, based on the analysis of physical indices, and then orthogonal tests were carried out to optimize the preparation. The results showed that the optimum preparation conditions were: mass fraction of portland cement clinker of 55%, Ca to Si ratio of 2.5, fly ash to pyrite cinder ratio of 1.0, and water to material ratio of 0.4. And then, 28-day compressive strength was 43.9 MPa. According to the national standard named as Common Portland Cement, the cement mark can reach the level of P·C 42.5.