Biochar of peanut shells and corn stalks was prepared in the shaftless-screw-conveying continuous pyrolysis reactor at 300, 400, 500℃. Measurements of proximate analysis and calorific value were carried out to obtain the composition and calorific value of biochar. Experiment on the adsorption property of methylene blue and iodine of biochar was carried out, and the respective correlations between absorption properties and RGB, grey value were explored. Results showed that with the increased carbonization temperature, the volatile content was reduced, the fixed carbon and ash content and the calorific value of biochar were increased. Methylene blue adsorption value and iodine adsorption value of biochar made at low pyrolysis temperature were larger than those at high pyrolysis temperature. It meant that adsorption characteristics of biochar at low pyrolysis temperature were better. With the increase of pyrolysis temperature, adsorption value and RGB value of biochar were declined. There was a strong positive correlation between adsorption characteristics and RGB value, and the correlation coefficient was ranged from 0.582 to 0.944. Analogously, the correlation coefficient of adsorption characteristic value and grey value was ranged from 0.685 to 0.977, which indicated that they also had strong positive correlation. A quick detecting method of carbonization level and adsorption properties of biochar was proposed.