BMI resin solution synthesized by using BMI resin and the solvent of acetone was mixed with CBN abrasive in proper proportion to prepare slurry, and then the whetstone was prepared with the process of casting, acetone evaporating and resin curing. The best dosage of the acetone was analyzed with the microstructure of the whetstone. Experiment results have shown that, when the content of acetone is under 16.9%, the CBN abrasive is not well-distributed in the BMI resin. However, when the content of acetone is 23.4%~29.0%, the CBN abrasive distributes uniformly. Nevertheless, as the content of acetone was up to 33.8%, the CBN abrasive deposits in the BMI resin. In addition, when the content of acetone is 23.4% and the BMI resin content is in the region of 7%~16%, the flexure strength and hardness of the whetstone are reinforced with the increase of the content of BMI resin. If the content of BMI resin is beyond 16%, it is difficult to volatilize the acetone as the viscosity of slurries increases, which results in the increase of the porosity and the decrease of the flexural strength and the hardness of the whetstone.