After activation and regeneration of the spore suspension of Streptomyces rimosus 186-6, a target strain named P-11 was obtained through compound mutagenesis of microwave and LiCl,random breeding,NTG-induced mutagenesis,breeding of resistance to its metabolic products,NaNO₂-induced mutagenesis,and screening of phosphate resistance.The fermentation titer of strain P-11 was higher than that of strain 186-6 by 20.75%.Strain P-11 was subcultured on slant for 5 times to study its hereditary capacity.Compared to the original titer,the fermentation titers of each generation of strain P-11 were 99.8%,100.2%,98.5%,97.4% and 96.6% respectively,which showed that strain P-11 had good genetic stability.Study on the features of strain P-11 indicated that the purity of strain P-11 was 98.4% and its phosphorus tolerability was improved.The metabolic parameters of strain P-11 declared that its early metabolism was lower than that of strain 186-6.To optimize the fermentation medium,response surface methodology (RMS) was used, and a new recipe, which contains starch 120g/L,soybeans meal 15.5g/L,cottonseed meal 5g/L,CaCO₃ 15g/L,(NH₄)₂SO₄ 14.5g/L,NaCl 4.7g/L,corn syrup 10g/L,KH₂PO₄ 0.1g/L,defrother 0.1g/L,CoCl 0.01g/L,and amylase 0.12g/L,was obtained.Compared to the original recipe,the new recipe increased the titer of oxytetracycline by about 25%.The results of the effects of amino acid on the titer of oxytetracycline indicated that Thr,Ser and Phe played an active role in improving the titer of oxytetracycline.