The invention relates to a high-concentration liquid boric 
fertilizer and a preparation method thereof. The preparation method comprises the following steps of: on the basis of taking oil as raw materials, adding the oil, strong base and water into a reaction tank, heating by steam under the stirring state, conducting 
saponification, cooling, standing for layering, removing higher 
fatty acid on the upper layer, adding 
boric acid into a base glycerin solution on the lower layer in proportion, heating and stirring for reaction, adjusting the pH value to be 7-8 by using the strong base, standing, cooling and packaging to obtain the high-concentration liquid boric 
fertilizer. According to the high-concentration liquid boric 
fertilizer and the preparation method thereof, the needed raw materials can be obtained simply and easily, the process is simple, the investment and the cost are low, the fertilizer can adapt to the demands of the conventional agricultural production and can be promoted widely. The liquid boric fertilizer prepared by the invention contains 100-110g / L of 
boron so as to be high in born content, achieves or exceeds the industrial standard of microelement water-soluble fertilizer, and has the advantages of being completely water-soluble, stable in performance, good in blending property and quick in absorption, and widely used for crops, improving the 
stress resistance of the crops, effectively preventing the phenomenon of 
boron shortage of the crops, promoting the flowering and protecting fruits, improving the quality and increasing the yield.