Diverse application scenarios in 5G and beyond wireless communication systems have introduced various requirements in code lengths and rates of channel codes. For the decoding of polar codes, especially the brief-propagation (BP) decoding, flexible configuration of codeword length is still not involved in current decoders. In this paper, a semi-folded decoding structure is proposed which can be reconfigured to support multiple codeword lengths. Up to 16 codes can be decoded in parallel and the utilization of processing units is no less than 87.5% for various codeword lengths. The peak throughput of 19.29 Gbps can be achieved by the proposed decoder in SMIC 55 nm CMOS technology.