In order to investigate the strain rate sensitivity of the mechanical properties of cement and asphalt mortar (CA mortar),the stress- strain compressive experiment of CA mortar at different strain rates was performed by means of a microcomputer- controlling electronic universal testing machine.The results show that the mechanical properties of CA mortar increase with the strain rate,and the strain rate sensitivities are attributed to the limit of the crack propagation velocity,the inertial effect of the lateral deformation and the horizontal restraint of the asphalt network structure.Furthermore,a constitutive relation of strain rates is established.The constitutive relation can accurately stimulate the peak strength and elastic modulus of CA mortar,and the multiple correlation coefficients of the fitting and experimental results in the whole deformation process are both greater than 0.93.It is also found from the analysis of the sensitivity of constitutive relation that,the higher the strain rate is,the lower the toughness and strain rate sensitivity of CA mortar will be.