The invention discloses a preparation method for nano magnesia solid alkali based on a doped lignosite and relates to a method for preparing nano magnesia in a liquid phase deposition method. According to the preparation method, lignin sulfosalt is used as a template agent and a surface active agent, nano magnesia solid alkali is prepared via the liquid phase deposition method and calcination at different temperatures, and the lignin sulfosalt cheap, innocuous and easy to get services as the template agent, as a result, a controllable preparation technique for the nano magnesia is realized, the common dispersity problem of nano material is solved, and the application performance and the catalysis performance of the nano magnesia are improved. The preparation method has the advantages of easy control, low cost, and simple and convenient process and procedures, the prepared nano magnesia solid alkali is high in base strength, and the preparation method is applicable to industrial production.