The invention provides a preparation method of a composite biocontrol bacteria preparation used for preventing and treating peanut diseases. The composite biocontrol bacteria preparation used for preventing and treating peanut diseases comprises Brevibacillus laterosporu-LX12 (preservation number is CGMCC 7420) and Bacillus subtilis-LX13 (preservation number is CGMCC No.8805). The preparation method comprises following steps: the above bacteria strains are activated, and LB solid culture medium is inoculated with the activated bacteria strains for 3d of culturing at 28 DEG C; beef extract peptone liquid culture medium is inoculated with prepared Brevibacillus laterosporu-LX12 fermented seed liquid and Bacillus subtilis-LX13 fermented seed liquid respectively, and fermentation is carried out for 1 to 2d at pH value ranging from 7.2 to 8.5 and temperature ranging from 30 to 40 DEG C so as to obtain bacteria solutions for production; and the bacteria solutions are mixed at a Brevibacilluslaterosporu-LX12 to Bacillus subtilis-LX13 volume ratio of 2:1 so as to obtain the composite biocontrol bacteria preparation. The composite biocontrol bacteria preparation possesses obvious treatmenteffects on crown rot, southern blight, and root rot. The solid state composite biocontrol bacteria preparation is capable of solving problems in peanut vine recycling, providing living space and nutrients for biocontrol bacteria, and improving soli quality.