The invention relates to a preparation method of nano-loess slurry, which comprises the following steps: 1. weighing loess powder with the grain diameter of 5-20 micrometers, ball grinding media and water according to a ratio by weight of 1: (5 to 8): (2.3 to 9), and pouring the loess powder, the ball grinding media and the water into a ball grinding pot; 2. weighing hydrophilic modified polyacrylic acid which accounts for 5-10 percent of the weight of the loess powder, pouring the hydrophilic modified polyacrylic acid into the ball grinding pot, and sealing the ball grinding pot; and 3. placing the ball grinding pot on a ball grinder at a rotational speed of 300-500 revolutions per minute, and dispersedly grinding for 8-15 hours to prepare the nano-loess slurry with the grain diameter of 20 nanometers to 100 nanometers. The nano-loess slurry prepared by the method has the characteristics of grain refinement, easy dispersion, good stability, and the like and has the function of releasing anions and far infrared rays.