Next generation wireless communication introduces ultra high speed and low latency requirements to baseband processors, especially for multi-user multiple-input-multiple-output (MU-MIMO) systems. Polar codes, as the channel coding scheme in the control plane of 5G eMBB scenario, still cannot satisfy the hardware implementation requirements of polar decoders for MU-MIMO systems. In this brief, a high throughput and low latency polar decoder is proposed for MU-MIMO systems. The decoding architecture is fully unfolded to maximize hardware parallelism, and is fully pipelined by decoupling the round-Trip scheduling datapath to enable simultaneous processing of multiple codewords. Besides, a hybrid decoding datapath is introduced by proposing complementary decoding units with mixed data representations to reduce hardware complexity. For (1024, 512) polar codes, a decoding throughput of 100.6 Gbps is achieved, and the latency is 0.43 us when 36 users are processed simultaneously.