Abstract: The disclosure includes a platinum-based alloy catalyst and a preparation method thereof, a membrane electrode and a fuel cell. The method for preparing the platinum-based alloy catalyst comprises the following steps: (1) preparing nano-sized alloy particles of platinum and 3d transition metal; (2) carrying out acid treatment on the alloy particles prepared in step (1); and (3) annealing the alloy particles treated in step (2). The size of the platinum-based alloy particles is controlled, an atom number ratio of platinum to transition metal in the platinum-based alloy is controlled, and then etching and dissolution of acid is combined so that an atom number ratio of platinum to transition metal is further controlled, subsequently annealing is carried out at high temperature. The prepared platinum-based alloy catalyst improves the stability and durability of the platinum-based alloy catalyst, which supports the large-scale application of the platinum-based alloy catalyst in the fuel cell.