Abstract: The invention discloses a temperature-resistant and anti-collapse multi-branched polymer fluid loss reducer and preparation method thereof. The main chain of the temperature-resistant and anti-collapse multi-branched polymer fluid loss reducer is composed of the following repeating unit (I): In the repeating unit (I): x:y:z=(20˜80):(20˜80):(2˜30); the R1 and R2 groups are alkylamines having a multi-branched structure. The beneficial effect of the technical scheme proposed in the present invention is: introducing cheap acrylamide branch monomer into the polymer monomer system of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, the preparation process is simple, the reaction conditions are mild, and the production cost is significantly reduced. At the same time, the polymerized monomer does not contain aromatic ring monomers and ionizable monomers, is environmentally friendly, and maintains excellent temperature resistance, salt resistance and anti-collapse properties.