Abstract: In view of the stereoscopic distribution characteristics of small cell networks, we take a fresh look at this problem using tools from 3-D PPP, and we develop a new general model based on 3-D space for uplink cellular networks. The main idea is modeling mobile and small cells as two separate spatial PPPs. First, we derive the mathematical expressions of the uplink coverage probability for the small cell networks. Then, based on the coverage probability, the closed expression of average uplink channel capacity a typical cell is deduced. Under general assumptions, the uplink coverage probability and channel capacity can be easily evaluated through fast integral calculation. We compare our model to the traditional 2-D model and actual mobile user/small cell deployment, and we observe that the proposed model is more accurate and provides a closer bound of coverage probability.