The invention discloses a p-methoxy cinnamic acid ester preparation method and belongs to the field of organic synthesis. The p-methoxy cinnamic acid ester preparation method comprises the steps that 1, p-methoxyaniline and 60-75 wt % of sulfuric acid solution are evenly mixed, 18-25 wt % of sodium fluoborate solution is dropped into the mixed solution at the temperature from 30 DEG C to 50 DEG C; 2, acrylic ester, surfactant and catalysts are added in the solution, and the solution is evenly stirred; 18-21 wt% of sodium nitrite solution is dropped into the solution during the stirring process, all the sodium nitrite solution is dropped in the solution for 30-60 minutes, the inner temperature is controlled within the range from 30 DEG C to 45 DEG C during the dropping process, and the temperature is kept and the reaction continues for 30 to 40 minutes after the dropping is finished; 4, the temperature is increased to 50 DEG C to 60 DEG C, and the reaction is conducted for 1-1.5 hours and then the reaction is over. According to the p-methoxy cinnamic acid ester preparation method, raw materials and the catalysts are low in cost and high in using efficiency, the operation is simple and pollution is little. In addition, an ordinary diazotization reaction needs to be controlled at low temperature, and the temperature for the p-methoxy cinnamic acid ester preparation method during the dizotization process is milder, the corresponding cooling cost is saved, and the p-methoxy cinnamic acid ester preparation method has wider industrialized application prospects.