The invention discloses a heat-source-free early strength polycarboxylate water reducer and a preparation method thereof. The method comprises the following steps: any one or more than two selected from a reducing agent, a chain transfer agent and an unsaturated acid derivative are mixed with water, such that a water solution with a mass percentage concentration of 44+/-3% is obtained, and is marked as an X material; unsaturated sulfonate and a monomer a are mixed with water, such that a water solution with a mass percentage concentration of 26+/-1% is obtained, and is marked as a Y material; unsaturated polyoxyethylene ether and water are added into a polymerization reaction kettle, and stirring is carried out until unsaturated polyoxyethylene ether is completely dissolved; an oxidizing agent is added and the mixture is well mixed; the adding of the X material and the Y material is started, and an adding time is controlled at 1-3h; when adding is finished, the temperature is maintained for 1-2h; the polymerization reaction is finished, and a product is neutralized with an alkali solution with a mass percentage concentration of 20+/-2% until the pH is 6-7. The method provided by the invention has the advantages of simple process, reduced cost, easy industrialization and no environment pollution. With the method, the water reducing rate of the water reducer is improved, and concrete early strength is improved.