The invention relates to a preparation method of fluorine-containing multipolymer which can be used for producing dope with excellent combination property, good stability and low cost. The preparation method of fluorine-containing multipolymer is as follows: 15-25 portions of metacrylic acid ester which is monomer, 5-10 portions of acrylic ester and 5-10 portions of functional monomer are performed with graft copolymerization reaction in solution of 10-20 portions of fluorocarbon resin which is soluble under normal temperature, and the structural formulas of the metacrylic acid ester, the acrylic ester and the functional monomer are respectively shown as (1), (2) and (3), wherein R1 and R2 which are mutually independent are alkyl with 1-4 carbon atoms, R3 is H, hydroxyethyl group or hydroxypropyl, and R4 is H or cymene. The invention has excellent combination property, can stably exist for a long time without being added with dispersion stabilizer and does not delaminate, thereby effectively lowers the cost of product.