DFE(Douchi fibrinolytic enzyme) is a new fibrinolytic enzyme which was discovered in Douchi. DFE is worthy developing as either natural thrombolytic agent or health food to prevent thrombotic diseases.The gene encoding pro-DFE from DC-12 was cloned and expressed in E. col.i The catalytic efficiency of DFE was improved by directed evolution. The mutant DFE was expressed in Bacillus subtiilis WB800 by induction with IPTG and the fermentation conditions were optimized. The main results of the thesis are as fol...