The blast furnace slag with extremely high discharge temperature is a by-product in iron and steel production process. Dry granulation method based on rotary disk atomizer shows great advantages in recovering sensible heat of blast furnace slag. However, during flight process, molten particles may impact on the wall which would greatly affect the stability of the device and the overall heat transfer efficiency. Moreover, during the deformation process of molten slag with high temperature and complex components, its physical properties change dramatically. In the current study, combining the volume-of-fluid method and solidification/melting model to track the free interface and deal with the phase change respectively, a three-dimensional symmetrical model was constructed to simulate the thermal process of molten particle collision. The solidification temperature range and variable physical properties were taken into consideration. As the results, the temperature and velocity distributions, spread factor, solidification time were obtained. And the effects of diameter, initial temperature, impact velocity of particles and initial temperature of the wall on the process were discussed. It was represented that a single slag particle impacting on the wall underwent process of spreading, retracting, and stabilizing. Two dimensionless correlations were developed to predict deformation behavior of slag particle and the maximum value of wall shear stress. Furthermore, the sequential impact of two slag particles with the same diameter was investigated and splashing and remelting occurred.