The invention discloses a process method for preparing high-purity levodopa. By utilizing chemical characteristics of levodopa, acid water is applied to extract, an impurity removing agent is used for preliminary purifying, and enriching and separating are carried out by virtue of electroosmosis; then, separation is carried out by adopting an isoelectric-point crystallization technology, and a crude crystal is dried to obtain a finished product after being re-crystallized. Process steps are as follows: crushing a mucuna material, adding acid water to extract, adding the impurity removing agent into extracting liquor to remove impurities, filtering, regulating pH value of the liquor to 1-4, entering an electroosmosis device for enriching and separating, regulating the pH value to 3.5, placing at a low temperature of 0 DEG C-4 DEG C, separating out levodopa, regulating acidity of precipitates, adding an antioxidant, placing at the low temperature, separating out crystal, and drying to obtain the finished product. The process method disclosed by the invention adopts the electroosmosis method for enriching and separating the levodopa, so that problems that the levodopa is damaged in an alkaline environment and the like are effectively avoided, and therefore, production period is shortened, energy consumption and cost are lowered; moreover, the method is environmental friendly.