Simulation of frost formation process on cold surface is carried out based on fractal theory combined with phase change dynamics. Before frosting, the phenomena of vapor condensation, droplet growth and frozen on cold plate are successfully simulated based on phase change dynamics and then a fractal simulation of the frost formation and growth process over the frozen droplets is carried out based on diffusion limited aggregation (DLA) model. The simulation results accord well with the experimental results. The time when the condensation droplets are present and frozen on the surface during simulation process is nearly the same as the experimental result. Before the droplets are frozen, the trend that the surface contact radius of the droplet varies with condensation time is similar to actual one. The simulation results also show that the thickness of frost layer is nearly equal to the measured value. By that means, the feasibility of this method of simulating the frost formation is verified and the new attempt made to foster the combination between fractal theory and phase change dynamics is of great significance. This study also provids a foundational theory work for a more reasonable and accurate frosting process model.