The invention relates to a synthetic method of the modified styrene butadiene latex special for the cementing slurry of oil-gas fields. The source material contains 30 to 50 portions of butadiene, 40 to 70 portions of styrene, 0.1 to 2 portions of unsaturated sulfoacid or the salt with functional monomer A bearing a carbon-carbon double bond, 0.1 to 3 portions of unsaturated carboxylic ether, unsaturated amide or unsaturated nitrile compound with functional monomer B bearing a carbon-carbon double bond, 0.3 to 4 portions of emulsifier, 0.4 to 2.5 portions of initiator, 0.2 to 0.6 portions of molecular weight regulator, 0.2 to 0.7 portions of electrolyte, 0.01 to 0.1 portions of chelon and 100 to 130 portions of soft water. The start PH value of polymer emulsion is 7 to 10. The polymerization temperature is 60 to 90 DEG C. The method comprises the steps of adding the soft water and the butadiene, the styrene, the initiator, the emulsifier and the molecular weight regulator by two steps; adding the functional monomers, the chelon and the electrolyte by one step when feeding. The styrene butadiene latex can prepare the stable latex cementing slurry.