The invention discloses an environment-friendly high-proportion r-ABS (Recycled ABS) flame-retardant modified composition and a preparation method and application thereof. The r-ABS flame-retardant modified composition adopts the formula as follows: 70 parts of r-ABS, 30 parts of high-rigidity ABS resin, 10-25 parts of an environment-friendly brominated flame retardant, 0-1 part of an antimonic flame-retardant synergist, 1-5 parts of a phosphorus-based flame-retardant synergist, 5-15 parts of a flexibilizer, 1-3 parts of a compatilizer and 1-5 parts of inorganic powder, wherein the environment-friendly brominated flame retardant is tri(tri-bromophenyl) cyanurate. The invention further provides a preparation method and preparation of the r-ABS flame-retardant modified composition. The r-ABS flame-retardant modified composition provided by the invention can still keep relatively high mechanical property and flame-retardant property after flame-retardant modification, and meanwhile is extremely low in cost. The r-ABS flame-retardant modified composition is suitable to be popularized and applied in various fields needing flame retarding, such as the fields of household appliances, transportation and communication.