In existing soft decision algorithms, a soft BCH decoders provides better error correcting performance but has much higher hardware complexity than a traditional hard BCH decoder. In this paper, a soft BCH decoder with both better error correcting performance and lower complexity is presented. The low complexity feature of the proposed architecture is achieved by dealing with least reliable bits. By compensating extra one error outside the least reliable set, the error correcting ability is improved. In addition, the proposed error locator evaluator evaluates error locations without Chien search, leading to high throughput. As compared with the traditional hard BCH decoder, the experimental result reveals that our proposed improved soft BCH decoder can achieve 0.75db coding gain for BCH (255,239) code. Implemented in standard CMOS 90nm technology, it can reach 316.3Mb/s throughput at 360MHz operation frequency with gate-count of 4.06K according to the post-layout simulations.