We have modeled the dust envelopes around carbon stars with close attention to the evolution of the structure of the dust shells. We use various dust density distributions to take account the effect of the superwind due to the helium shell flash by adding a density increased region. Depending on the position and quality of the density increased region, the model results are different from the results with conventional density distribution. The new results fit the observations of some carbon stars better. The IR two-color diagrams comparing the results of the super wind models and IRAS observation of 252 carbon stars have been made. The new results can explain much wider regions on the IR two-color diagrams.