Abstract: Abstract: Soil water content measurement is an important and tedious task, and the ground penetrating radar (GPR) technique has been used for soil water content distribution estimation. The GPR is a fast and nondestructive tool, capable of providing information of electromagnetic wave propagation. The conventional methods of GPR for detecting soil water content mainly include the air direct wave method, the surface direct wave method, the reflected wave method and the borehole GPR method. Because the electromagnetic wave attenuation in aqueous medium is fast, the air direct wave method and the surface direct wave method can only detect the soil water content near the surface, and these models are vulnerable to interference, and difficult to determine the zero take-off time, so the detection results are always not accurate. Reflection wave method is widely used at present, but it requires clear reflector in the scope of radar wave propagation, and it is difficult to apply in complex underground area. The borehole GPR is mainly suitable for the detection of soil moisture content in small scale. The radar wave average envelope amplitude (AEA) method is to find out the radar average amplitude envelope signal value having the best correlation with the shallow strata dielectric constant by analyzing and establishing the relationship between the radar early-time average amplitude envelope signal value and shallow strata dielectric constant. The instantaneous amplitude has been computed by considering the amplitude of the Hilbert transform of signals simulated by a typical common-offset configuration, using the value of average envelope amplitude calculated in different early-time windows to back calculation the dielectric constant, then the Topp formula is used to calculate the soil water content. In order to assess the accuracy of GPR in detecting the surface soil moisture content, early-time ground penetrating radar signal AEA method is used to detect the sandy soil with water contents of 0.05, 0.15 and 0.25 cm3/cm3 in laboratory. Comparing the water contents derived by AEA and Time domain reflectometry it shows that the root mean square errors are 0.026, 0.015 and 0.01 cm3/cm3, and the effective detection depths of AEA method are 0.9, 0.6 and 0.3 m, respectively, and with the increase of water content, the detection accuracy of AEA method increases, but the detection depth decreases sharply; when water moisture content is small, the detection depth of AEA method increases, while the detection error also increases accordingly. Field detection is conducted at the same time. Comparing the water content derived by TDR and drilling sampling and AEA, it indicates that, within a certain accuracy requirement, AEA method can get the similar soil water content with TDR and drilling sampling, and is able to get soil water content and distribution state for large area fast, accurately and continuously. It is feasible to detect the shallow stratum soil moisture content by using the method of early-time ground penetrating radar signal AEA.