A new mathematical model，the two-step diffusion model with three adjustable parameters，was developed based on the diffusion model and the lumped parameter model. Both internal diffusion resistance and solid solute internal wall resistance were considered to make the model a good description to supercritical fluid extraction (SFE) process. The supercritical CO2 extraction of clove oil is simulated. The comparison with the experimental data indicates that the values of AARD are between 2.33% and 19.48% under different experimental conditions，and the overall value of AARD is 8.09%. The experimental data for clove oil are also used to compare with the simulation by the diffusion model and the lumped model，and the overall values of AARD are 17.51%，8.13%，respectively，so the two-step diffusion model is better for simulating the process of supercritical CO2 extraction of clove oil.