The present invention relates to mixed bacteria producing a biological surfactant, and a screening method thereof, wherein the mixed bacteria is formed by mixing three strains, and the three strains respectively are Pseudomonas stutzeri having the preservation number of CCTCC AB 205091, Nocardioides ginsengagri having the preservation number of CCTCC S2013441, and Bacillus licheniformis having the preservation number of CCTCC AB 205141. According to the present invention, oil extraction strains to be screened are selected, the selected oil extraction strains to be screened are activated and cultured, the activated and cultured oil extraction strains to be screened are subjected to primary screening by using a blood flat plate method to obtain a primary screening fermentation broth, and the primary screening fermentation broth is re-screened by using an oil ring removing method so as to obtain the mixed bacteria; and the mixed bacteria integrates the advantages of the three stains and can produce the biological surfactant capable of being applied in the oilfield oil extraction, and the screening method has characteristics of wide application range, effective screening cost reducing, high accuracy, strong selectivity, simple process, easy operation, and short period compared with the prior art.