The invention discloses a preparation method of a Pd/Ag nano-alloy catalyst for a direct ethanol fuel cell. The method comprises steps as follows: alcohol is added to water in the volume ratio of alcohol to water being (3-7):1, the mixture is stirred and sequentially mixed with polyvinylpyrrolidone, a metal palladium chloride precursor, a metal silver salt precursor and sodium citrate, the mixture is stirred at the temperature of 20-25 DEG C for 1.5-2.5 h and reacts for 1.8-12 h under a light condition, centrifugal separation is performed, precipitates are collected, washed and dried, and the Pd/Ag nano-alloy catalyst can be obtained. Polyvinylpyrrolidone is taken as a stabilizer and a guiding agent, the Pd/Ag nano-alloy catalyst is synthesized in one step under a mild condition by the aid of the reducing action of alcohol and sodium citrate, the synthesis efficiency is improved, the yield is increased, besides, the morphology of the catalyst has controllability, the catalyst has better catalytic activity for ethanol and can be used for the direct ethanol fuel cell, the preparation process is simple, the production cycle is short, large-scale production is easy to realize, and the catalyst has good application prospects.