Abstract: With more and more space activities such as manned space operations and space station missions, concern with hazards of small-size space debris, especially those of 1-10 cm, is increasing. Limited by sensor sensitivity and data processing capability, they cannot be routinely tracked or cataloged. Therefore, statistical characterization technique is relied on to acquire knowledge on small-size space debris, i.e. to estimate population and distribution of them. Based on a simplified phased array radar fence for space debris detection, a method for estimating space debris population and distribution in altitude and inclination using statistical technique is proposed. The method uses only orbit altitude and inclination data measured and the time of debris crossing the radar fence, and does not depend on a priori information of space debris environment. Because of the relatively sparse distribution of space debris, the problem whether one debris object that may be detected by the radar fence （i.e. inclination and radar cross section are large enough） actually crosses it can be modeled as a Poisson process. For debris objects in a given altitude or inclination bin, the average rate of crossing the radar fence is derived. A companied company with the average crossing rate measured, space debris population in the given altitude bin or inclination bin is obtained. Then the total number of debris objects and their When radar cross section data can be secured, distribution in altitude and inclination are acquired. the method can also be used to estimate space debris population distribution in size. The simulation results show the validity of the proposed method.