In order to study the dynamic mechanical properties of 40 MPa cement mortar with initial porosity, the impact compression tests of cement mortar material under seven different velocities were conducted using a powder gun. The samples timevoltage waveforms were recorded based on PVDF pressure sensor and then the corresponding timepressure waveforms were derived. The stress waveforms of different position found in the experiment indicate that the stress wave is on rapid rise to the peak then decays with time and the propagation distance. It illustrates that cement mortar material has obvious rate sensitivity, viscoelastic and energy dissipation characteristics, and the attenuation of stress wave can be attributed to the microdamage defects inside the material. Then, through further analysis of the experimental data, the shock Hugoniot relationships were determined, which is a linear relationship between the shock wave speed and the wave particle velocity, and densitypressure shock Hugoniot relationship were described by the experimental data. On the other hand, the Hugoniot elastic limit (HEL), the initial elastic wave velocity and the wave velocity of granular material were obtained. Moreover, the Pα equation of state (EOS) and highpressure polynomial Grüneisentype EOS for cement mortar considering initial porosity compaction was given, and the material parameters in the EOS were fit.