Abstract: The present invention provides a flame-retardant yarn/fabric/clothing, containing the following three types of fibers in percentage by weight percent based on their total weight: modacrylic: 20% to 80%; cellulose: 10% to 50%; and polyimide: 1% to 50%. A vertical burning test is carried out in accordance with GB/T 5455-2014 to test the flame retardance of the flame-retardant yarn, fabric or clothing in the present invention, and the measured char length is lower than 150 mm, 100 or 50 mm. The char length is reduced to different extents, and thus different flame retardance requirements are met.