Objective From the Maxwell-Wagner theory for suspensions of spherical and the electrical property of blood,an equation has been derived to calculate RBC aggregate radius,a new method based on the impedance spectroscopy analysis has been developed to evaluate the Red Blood Cell (RBC) aggregation property. According the new method,the impedance spectroscopy of blood has been measured at first with the multi-frequency technique,then to get the impedance - frequency curve by a fit method,the time constant T has been extracted from the curve,at last,the RBC aggregate radius R has been gotten. According to the changes of R during the RBC aggregation,the measurement and evaluation of RBC aggregation property can be realized. The impedance spectroscopy analysis method introduced in this paper is a new,effective method to study RBC aggregation.