The invention discloses a preparation method of a soap-free emulsion type carboxyl/ester-based emulsion polymer for a coating. According to the invention, carboxylic acid monomers and ester monomers are used as raw materials, and a soap-free emulsion polymerization method is employed, meanwhile, a pH regulator is used for controlling the pH value of the reaction environment to be 8 to 8.5; the preparation method comprises the following steps: adding soap-free carboxyl hydrophilic monomers; according to the present invention, the soap-free ester-based hydrophobic monomer and the initiator a aresubjected to a reaction to synthesize the soap-free polymer, and the soap-free polymer and other raw materials are subjected to a reaction to synthesize the polymer waterproof coating material. The preparation method has advantages of rapid polymerization speed, less reaction steps, less environmental pollution and mild reaction conditions, and the synthesized product has characteristics of goodflexibility and high elongation at a low temperature.