The invention discloses modified composite barite for a 
drilling fluid. The barite is prepared from composite barite, a modifier 
sodium hexametaphosphate, an acrylic 
copolymer, octylphenol ethoxylate-30 and 
polyethylene glycol 400. According to the modified composite barite, on the basis that ultrafine barite and baryto 
calcite are compounded, an acrylic 
copolymer hyperdispersant is prepared fromsodium hexametaphosphate and 
phthalic anhydride, 
acrylic acid and n-butyl 
alcohol as monomers to improve the surface property of 
a weighting agent, furthermore, surfactants octylphenol polyoxyethyleneether-30 and 
polyethylene glycol 400 are used as auxiliary materials to further enhance the hydrophilic dispersion performance, and thus the modified composite barite is prepared, the modified composite barite is suitable for a water-based drilling and completion fluid, the suspension property is excellent, and the 
density reduction rate of a weighted 
drilling fluid system is lower than 3%; the acid 
solubility is greater than or equal to 45%; the 
viscosity coefficient of a 
drilling fluid system filter cake is lower than that of conventional barite by 30% or above; and the 
apparent viscosity change rate before and after the 
calcium sulfate is added is less than or equal to 3mPa*S.