The impact of downlink co-channel interference (CCI) is increasingly highlighted in heterogeneous networks (Het-Nets) where the macrocell base stations (MBSs) and low-power nodes share the same spectrum resource. In this paper, we focus on mitigation of downlink CCI from MBS to picocells, which are severely affected, through the application of coordinated beam forming (CBF) technique. The closed-form expressions of average throughput for an arbitrary user with and without using CBF are derived, where a trade-off is observed between suppressing the CCI to picocells and increasing the throughput of the macrocell. Furthermore, to maximize the HetNet throughput, two adaptive algorithms are proposed to determine the CBF set of picocells based on the instantaneous throughput and the average throughput, respectively. The analysis of average throughput is validated by simulation results, and total throughput of the HetNet is improved by use of our proposed algorithms.