The present invention belongs to the technical field of warning for petroleum pollution, and particularly provides an early warning method for vadose zone and groundwater pollution in a contaminated site. The present invention can monitor and analyze the conductivity and water content of pore water in a vadose zone in real time and determine the pollution level according to a parameter variation and an analysis on collected samples; and furthermore, the present invention can give multi-level early warnings before groundwater is polluted, accurately determine the pollution level, and provide corresponding measures in time.