The invention discloses a self-support mesoporous gold-palladium alloy film electrochemical synthesis ammonia catalyst which is prepared from the following steps: soaking a piece of foamed nickel of which the area is 0.1-6cm<2> into a hydrochloric acid solution, and removing surface impurities; respectively preparing a 5-50mM chloroauric acid solution and a 5-50mM chlorine sodium palladate solution; weighing 2-20mg of PS-b-PEO, dissolving the PS-b-PEO into 1-5mL of tetrahydrofuran, adding 1-3mL of absolute ethyl alcohol, 0.5-2mL of the chloroauric acid solution and 0.5-2mL of the chlorine sodium palladate solution, preparing a reaction solution, and putting treated foamed nickel into the reaction solution; soaking the foamed nickel into isopropanol to remove a surfactant and an unreacted metal precursor, and performing washing and drying, so as to obtain the self-support mesoporous gold-palladium alloy film electrochemical synthesis ammonia catalyst. The invention further provides a preparation method of the self-support mesoporous gold-palladium alloy film electrochemical synthesis ammonia catalyst. The catalyst disclosed by the invention has outstanding catalysis activity and stability in electrochemical synthesis ammonia reactions.