Abstract: In this paper, we provide a scheme which can transform 3D beamforming into finding optimal antenna downtilt, specific to 3D multi-user MIMO Networks based on larger scale fading. First, we use Max Ratio Transmission(MRT) precoding. We assume desired signal power, inter-user interference power and inter-cell interference follow the Gamma distribution, then we can formulate an optimization to maximize system throughput in relation to antenna downtilt. Finally, we proposed an improved quantum bacterial foraging algorithm(QBFO) to find its solution. Simulation result shows that proposed scheme has higher achievable sum-rates compared with zero-forcing (ZF) precoders in lower SNR and better performance using QBFO.