In this paper, we investigate how picocells overlaid in macrocells expand their coverage areas under different Cell Range Expansion (CRE) strategies in a macro-pico heterogeneous network. Through system level simulations, the relationships among the presented CRE strategies are specified from both qualitative and quantitative perspective, in which network topologies using different CRE strategies are displayed, and load balancing performance is compared in terms of CRE user ratio. Relatively good CRE strategies are derived from statistics. Furthermore, as CRE will largely decrease network throughput due to unexpected interference on the downlink path from Macrocell Base Stations (MBSs) to CRE users, we then apply Coordinated Multi-Point (CoMP) transmission in heterogeneous deployment to deal with the inter-cell interference. Intensive simulations show that CoMP could significantly improve both cell average Spectrum Efficiency (SE) and 5% cell edge SE, and a recommended value of CoMP bias which decides CoMP user ratio is given at last.