Four pyrolysis temperatures (300 ℃, 400 ℃, 500 ℃, 600 ℃) semi-coke were selected, and the microstructure of oil shale semi-coke was analyzed by scanning electron microscopy (SEM), and then equal masses of oil shale semi-coke (0%, 5%, 10%, 15%, 20%, 25%) were used to replace cement. The standard consistency water requirement, the fluidity of mortar and the flexural and compressive strength of cement sand at different ages were tested. The results show that the semi-coke of oil shale is lamellar and porous. With the increase of pyrolysis temperature, the number of micropores and small pores gradually decreases, and the number of medium and large pores increases. Adding oil shale semi-coke increases the water requirement of standard consistency and reduces the fluidity of mortar. There is a strong linear relationship between the content of oil shale semi-coke and the water requirement of standard consistency. With the increase of the pyrolysis temperature of oil shale semi-coke, the flexural and compressive strength of cement sand increases first and then decreases, and the mechanical properties reach the best at 500 ℃. With the increase of the amount of oil shale semi-coke, the flexural and compressive strength of cement sand gradually decrease. When the oil shale semi-coke content is 15%, the mechanical properties of the 56 d pyrolysis semi-coke cement sand at 500 ℃ are close to that of the P·Ⅰ 42.5 benchmark cement sand.