The invention discloses an oil field neutral antiscale agent for barium sulfate and strontium sulfate scale and a preparation method thereof. The antiscale agent G comprises the following components by mass: 50-55 parts of maleic anhydride-A, 15-30 parts of acrylic acid-B, 15-35 parts of methyl acrylate-C, 10 parts of ammonium persulfate-D, 150 parts of distilled water-E, and a 50% sodium hydroxide aqueous solution F. The preparation method of the antiscale agent G includes: (1) adding A into E, stirring the materials evenly at 50DEG C till A is completely hydrolyzed; (2) adding D into E, mixing the materials evenly till D is completely dissolved; (3) adding the mixed solution of B and C and the aqueous solution obtained in step (2) dropwise into the aqueous solution obtained in step (1) simultaneously for 15min, then raising the temperature to 85DEG C and carrying out reaction for 4h, thus obtaining a light yellow viscous liquid; and (4) adjusting the pH value of the light yellow viscous liquid obtained in step (3) to 7, thus obtaining the antiscale agent G. The neutral antiscale agent provided by the invention almost has no corrosion to pipelines, is non-toxic, and can effectively solve the problem of serious scaling phenomenon of oil field shafts and stratum.