The invention belongs to the field of 
chemical engineering, and relates to a preparation method of a water-retention and 
nitrogen-fixation slow release water-soluble 
fertilizer. The method comprises the following steps: preliminarily mixing a 
nitrogen fertilizer, a high-molecular material, a water retaining agent and a filler, adding above preliminarily 
mixed materials to a 
solid-liquid mixer, continuously stirring and mixing the preliminarily 
mixed materials, adding water and auxiliary agents at a constant stirring rate, carrying out preliminary kneading, adding the above obtained mixture to an extruding and kneading device, adding water, carrying out secondary kneading to prepare a paste, continuously sending the paste to a granulator, granulating the paste, 
drying prepared granules, sieving the dried granules, and packaging the sieved granules to obtain the final water-retention and 
nitrogen-fixation slow release water-soluble 
fertilizer. The high-molecular material 
polyacrylamide is effectively added to a chemical fertilizer in order to reduce soil 
erosion and effectively improve the 
soil structure, so the total 
porosity and the 
capillary porosity of the soil are increased, and the soil capacity is reduced, thereby soil granules and the pore structure keep stable. Polypropionamide substantially inhibits the loss of the nitrogen element and improves the 
nitrogen fertilizer utilization rate.