Abstract: In order to investigate the effect of thermally activated oil shale semi-coke on the mechanical properties of concrete, oil shale semi-coke after high temperature calcination at 300 ℃, 400 ℃, 500 ℃ and 600 ℃ was selected. Semi-coke concrete was prepared by replacing cement with 5%-25% of the oil shale semi-coke. The compressive and flexural strengths of the semi-coke concrete were tested. The internal pore information of the semi-coke concrete was analyzed by nuclear magnetic resonance, while the relationship between the strength and porosity of the semi-coke concrete was studied. The results showed that with the increase of the calcination temperature for the oil shale semi-coke, the compressive and flexural strengths of the semi-coke concrete first increased and then decreased, with the optimal mechanical properties at 500 ℃. With the increase of the oil shale semi-coke content, the compressive and flexural strengths of the semi-coke concrete first increased and then decreased, where the optimal mechanical properties were achieved at a semi-coke content of 15%. The internal structure of the semi-coke concrete had many small pores. The porosity of the semi-coke concrete first decreased and then increased with the increase of the oil shale semi-coke content, where the minimum porosity was obtained at a semi-coke content of 15%.