Using sludge at the bottom of Hengshui Lake as samples, and screened out the SJ-9 strain with PHA synthesis capability by enrichment, purification, Nile blue staining, far-infrared spectroscopy and gas qualitative and quantitative analysis. The infrared scanning of SJ-9 bacteria product showed that this product was middle chain PHA. Optimization of SJ-9 fermentation conditions obtained the optimal conditions with optimal carbon source of sodium butyrate, optimal C/N of 35, optimal fermentation time of 120 h, and optimal initial pH for culture substrate of 7.0. 10 L fermenter amplification culture under these conditions showed consistent results with flask culture, and the bacteria and PHA had the highest yields at 120 h, with the maximal yields of 6.81 and 2.36 g/L, respectively.