Abstract: Due to highway which has been exposed to sun ,wind and rain, it忆s easy to lead the formation of water under the road causing crack. As time passes, the distortion of highway subgrade is caused and is harm to road health. In reaction to phenomenon, a method that is detecting hydrous heteroplasmon under road based on time reversal by GPR is proposed. First, the green function by reflection and transmission of electromagnetic wave of layered media to original data to preprocessing by fundamental time reversal theory is amended, and then reach to resolution enhancement of target, finally finish the detection of hydrous hetero-plasmon under highway by BP imaging algorithm. The accuracy of theory is validated by the actual measurement data.