In this study, calcined coal series kaolin with high oil absorption value was prepared from coal series kaolin (Shuozhou, Shanxi province) by using aluminum fluoride trihydrate (AlF3·3H2O) additive which promotes the growth of mullite whiskers and subsequent ultrasonic crushing treatment. The effect of particle morphology on the oil absorption value of the powder was subsequently analyzed. The mechanism of AlF3·3H2O increasing the oil absorption value of calcined coal series kaolin was analyzed by scanning electron microscopy, X-ray diffraction and specific surface area analyser. The results show that the addition of AlF3·3H2O produces a large amount of mullite whiskers on the particle surface of the calcined coal series kaolin, and the submicron mullite whiskers on the particle surface significantly increase the oil absorption value of the samples. In addition, ultrasonic treatment of the samples can further increase their oil absorption values. When the ultrasonic treatment time is 45 min, the oil absorption value reaches 86.14 g/100 g. The circularity of the particles has a great influence on the oil absorption values of the powders. The circularity of the calcined coal series kaolin with high oil absorption values is generally lower than that of the ordinary calcined coal series kaolin, and the distribution of circularity is more concentrated.