Millimeter wave (mmWave) offers Gbps-level wireless services thanks to its huge spectrum and spatial utilization in the next fifth-generation (5G) wireless networks. Due to attenuations of signal loss, beam-based directional transmission is thus significant to overcome physical disadvantages. For multiuser service demands, the base station is capable of transmitting multiple high-gained beams via the massive antenna deployment. To simultaneously support a large number of users in a hotspot with finite beams, clustering is needed which several user groups are scheduled for each beam. To mitigate inter-beam interferences, we partition the original non- convex and nonlinear problem into two parts and propose the orthogonal beam clustering (OBC) and iterative power allocation (IPA) schemes through gradient descent method. Simulation results demonstrate that the groups with larger beam gains tend to be assigned with more power in order to provide higher rate. It also achieves better performance with increments of the orthogonal beam resources. Our proposed scheme can supports Gbps- level per user throughput which is twice higher compared to existing literatures.