In this study, a method to enrich forsythiaside A (FA) from the ball-milled powder of Forsythia suspensa leaves was established. Forsythiaside A was extracted by heating and stirring, and the extraction process was optimized by response surface methodology using the independent variables of extraction temperature, extraction time, liquid-to-material ratio, ethanol concentration, and pH value of the solution, respectively. Then five types of macroporous resins with different polarities were studied to explain the adsorption mechanism by static adsorption and desorption experiments. Different models were used to study the static adsorption thermodynamics and kinetic process of AB-8 resin on FA extracts, and optimal conditions of the process were optimized. Finally, the antioxidant abilities of purified FA were evaluated. The results showed that the optimum extraction conditions were 2.2 h, 53.4 °C, 45.7 mL/g, 60% ethanol, and pH 6, and the extraction efficiency of forsythiaside A could achieve 120.96 mg/g. The AB-8 macroporous resin was the most suitable resin with high adsorption and desorption rates. It was found that the Temkin model was able to calculate the adsorption parameters accurately. The adsorption kinetic process of the resin was in accordance with the pseudo-second-order kinetic model. The optimal process conditions were as follows: the optimum loading concentration of 5.83 mg/mL, the loading rate of 1 BV/h, and the loading volume of 7.51 BV; in the desorption process, deionized water was used to remove impurities first, and then, 30% ethanol was used with an elution rate of 1 BV/h. The purity of FA increased from 20.52 to 81.58%. The purified FA exhibited superior scavenging ability for DPPH radicals and ABTS radicals. Cytotoxicity experiments proved that it was safe and nontoxic and was capable of promoting cell growth. In conclusion, the present study provides a theoretical basis for industrially extracting and purifying FA on a reliable basis.