In-situ soil remediation mechanism through the vertical drains (VDs) is analyzed with numerical model as the error and complementary error function. Results from in-situ test and analysis indicate that the contaminant concentration ratio as initial one ( C/$C_0$) increases as the radius ratio ( r/R) increases from the injection well, and also increases as the depth ratio ( z/ H) increases from the top of contaminated area. The elapse time needed to attain $50\%$ and $90\%$ clean up level ($ t_{50},;t_{90}$) increases as the radius ratio ( r/R) and the depth ratio ( z/ H) increase. As above results, the procedure of soil flushing in contaminated area using vertical drains makes progress from the top of injection well to the bottom of extraction well.