Abstract: Abstract: The blend ratio of biochar and fast-release fertilizer (urea and potassium chloride, respectively) and the content of bentonite binder may influence the physicochemical and slow-release properties of biochar-based fertilizers particles. Experiments were carried out under 2 conditions: 1) biochar fertilizer ratio of 1:4, bentonite binder mass ratio of 5%, 10 %, 15% and 20%, and 2) bentonite binder mass ratio of 10%, biochar fertilizer ratio of 1:6, 1:5, 1:4 and 1:3. Based on corn straw biochar, cylindrical biochar based fertilizer particles with urea and potassium chloride were prepared by flat mold extrusion device. Their mechanical properties, surface functional groups, surface topography, soil column leaching properties, pH value and conductivity of biochar-based fertilizers were analyzed. The results showed that the average compressive strength of biochar-based particles urea and potassium chloride were higher than 200 N, greater than that prepared by pan granulation technique. The nutrient leaching rates in the first 3 days were lower than that of pure urea and potassium chloride. It meant that they had good mechanical properties and certain slow-release effect. The average compressive strength of biochar-based fertilizer particles of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer for the 4 different contents of bentonite were significantly different (P<0.05). The high content of bentonite binder and the low biochar and fertilizer content would lead to closer microstructure, more uniform composition distribution, and fewer surface pores. The mechanical properties and slow-release properties were better. When the mass fraction of bentonite binder was 20%, the average compressive strength of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer were the maximum value of 286.78 and 281.27 N, respectively, the nutrient leaching rate of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer in the first 3 days were the minimum value of 45.53% and 36.87%, respectively. The high biochar fertilizer ratios would result in the better slow-release performances. When the biochar fertilizer ratio was 1:3, the nutrient leaching rates of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer particles in the first 3 days were the minimum values of 42.06% and 40.32%, respectively. The pores on the surface of potassium chloride biochar fertilizer particles increased first and then decreased. When the biochar fertilizer ratios were 1:6 and 1:3, the average compressive strength were 271.25 and 282.42 N, respectively, but the relative standard deviation of the average compressive strength at 1:3 was the maximum. The pores in the internal structure of urea biochar-based fertilizer particles gradually increased. When the biochar fertilizer ratio was 1:6, the average compressive strength was the minimum values of 267.84 N. At the same time, the electrical conductivity of potassium chloride biochar-based fertilizer leachate and the pH value of urea biochar-based fertilizer leachate were similar to their respective nutrient leaching rates in change rule, which could be used for prediction of their nutrient leachate trends. Thus, the formulation of biochar-based fertilizer with the mass fraction of bentonite binder and the ratio of carbon to fertilizer of 20% and 1:4 or 10% and 1:3 are suggested to meet medium fertilizer concentration.