The feasibility of application of AC impedance spectroscopy（ACIS） in the detection to cement paste crack was assessed according to the previous work. The equivalent circuit model for describing ACIS properties of cement paste with crack was put forward based on Randles circuit. Using the steel as electrode, three groups of cement paste specimens with or without crack were tested for the peak to peak values of voltage signal according to the AC impedance spectroscopy testing technology. The dimension of crack designed in the cement paste varied to investigate crack dimension effect on electrochemical impedance properties of the specimens. Impedance amplitude for each specimen was figured out, and the experimental data was used to validate the equivalent circuit model. Results show that impedance amplitude for specimens with or without crack is quite different; there is quantitative relation between impedance characteristics and crack geometry scale.