To explore the effects of rock block proportion (RBP) and the shape on the mechanical properties of cemented soil-rock mixture (CSRM) that widely exists in nature, a series of large scale triaxial tests is conducted in laboratory. Firstly, specimens of soil-rock mixture mixed with cement and without cement are compared to demonstrate that soil-rock mixture is necessary to be further divided into CSRM and uncemented soil-rock mixture. Then, contrast tests are designed and performed on CSRM specimens with different RBPs and rock block shapes. Finally, the effects of RBP and shape on the mechanical properties of CSRM are analyzed. The results indicate that CSRM specimens with 3% cement exhibit evident strain softening band and localized shear band, whose strength and modulus are greatly increased compared with those of specimen without cement. Under given conditions, peak strength and brittleness index both decrease with increasing RBP. With 40% RBP, the peak strength of CSRM specimen with gravel blocks is slightly lower than that of CSRM specimen with pebble blocks; while the residual strength is slightly greater. With 70% RBP, no matter the peak strength or the residual strength of CSRM specimen with gravel blocks is greater than those of CSRM specimen with pebble blocks, especially under higher confining pressure.