Various types of small cell base stations (SBSs) are deployed randomly in heterogeneous small cell network to meet the soaring growth in traffic, which leads to more and more complex network topological structure and resource management. In this paper, we analyze the coverage performance and energy efficiency of a two tier heterogeneous network which is composed of micro tier and pico tier. With the aid of stochastic geometry tools and PPP properties, the analytical expression of success probability for each tier is derived to evaluate the tier's coverage performance how to vary with the SBS d...