Abstract: The paper aims to optimize the preparation process of biochar and obtain biochar products with high performance and low cost. In this study, biochar was made from walnut shell. The authors studied the effects of the carbonization temperature, activator types, activation time, activation temperature and activator concentration on iodine value and methylene blue adsorption value, furthermore, compared the results after carbonization and activation. The results showed that the activator type was the main factor affecting the properties of biochar. The optimal preparation condition was taking phosphoric acid as activator, liquid-solid ratio of 2:1, activator concentration of 50%, activation temperature of 400℃, and activation time of 120 min. The products after activation have well-developed pore, high specific surface area and inta