Abstract: Control effects of tank-mixing or alternate application of Bacillus subtilis BAB-1 AS, B. amyloliquefaciens SAB-1 AS, 1-O-acetylbritannilactone EC with synthesized fungicides on the development of cucumber diseases were investigated in fields. The trial conducted in Shouguang included the following treatments: alternate or mixing application of synthesized fungicides with different action modes and control spectra, such as boscalid 50WG, fluopicolide·propamocarb hydrochloride 68.75SC, pyraclostrobin·metiram 60WG, pyrimethanil 40SC, dimethomorph 50WP, difenoconazole 10WG, dimethomorph·mancozeb 69WP, famoxadone·mancozeb 68.75WG, famoxadone·cymoxanil 52.5WG; mixing application of biocontrol agents BAB-1AS, SAB-1AS with synthesized fungicides significantly effective to downy mildew, such as fluopicolide·propamocarb hydrochloride 68.75SC, dimethomorph 50WP, mandipropamid 25SC, pyraclostrobin 25 EC; alternate application of tank mixtures of BAB-1AS, SAB-1AS and synthesized fungicides with tank mixtures of different synthesized fungicides. The three treatments gave control efficacy of 94.5%, 92.3% and 93.6% for downy mildew, 90.7% 89.9% and 90.4% for powdery mildew, and 69.3%、85.6% and 85.7% for gray mould. Area under the disease progress curve (AUDPC) of each disease between the three spray programs is not significantly different. In the trial conducted in Dingzhou, mixing application of synthesized fungicides with SAB-1AS resulted in a much higher control efficacy (84%) for powdery mildew than that(72.8%)resulted from by mixing application of synthesized fungicides with BAB-1AS, and much lower control efficacy(61.3%)for gray mould than that(95.1%)resulted from the latter. Alternate application of synthesized fungicides with SAB-1、BAB-1 gave a significant control of powdery mildew, gray mould and downy mildew with efficacy of 90.2%, 89.3% and 92.6%, respectively. In the trial conducted in surburb of Baoding, alternate application of 1-O-acetylbritannilactone EC with synthesized fungicides, BAB-1AS, SAB-1AS significantly lowered severity and AUDPC of downy mildew, powdery mildew and gray mould, with the control efficacy of 83.5%, 87.4% and 88.5% and AUDPC of 219,352 and 249, respectively, and delayed the development of the three diseases.