The invention belongs to the field of preparation of modified silicone oil, and relates to a flame-retardant modified silicone oil, a preparation method thereof, and an application thereof in textileproduction. The modified silicone oil is mainly prepared through a copolymerization reaction of (perbromo-1,2-phenylene)dimethanol, trimethylol melamine resin, 1,4-dibromo-2,3-butylene glycol, hexaethylcyclotrisiloxane, methyldichlorosilane, 3-aminopropylsilane triol, ethylenediamine tetramethylenephosphonic acid and 1,3-bis(trimethylsilyl)urea. Monomers with high content of flame-retardant elements, such as bromine, nitrogen and phosphorus, comprising (perbromo-1,2-phenylene)dimethanol, trimethylol melamine resin, 1,4-dibromo-2,3-butylene glycol and ethylenediamine tetramethylenephosphonic acid are used as main copolymerization raw materials, and are copolymerized with an organosiloxane raw material to obtain the modified silicone oil. The obtained modified silicone oil has an excellent flexible performance, also has an excellent flame retardant performance due to the high content of the flame retardant elements comprising bromine, nitrogen and phosphorus, can be applied to textiles of machine-made bleached twill pure cotton clothes, and has an oxygen index reaching 32% or above.