The invention discloses a method for detecting soil mass cracking depth. The method comprises the following steps: distributing paired electrodes in layers in a soil mass to be detected; respectively measuring conductivity values among the paired electrodes in each layer of the soil mass by using a conductivity meter; drilling and irrigating among the paired electrodes in each layer of the soil mass, and measuring the conductivity values among the paired electrodes regularly by the conductivity meter; drawing curve graphs of soil mass conductivity values in different moments along with depth variation according to the measured conductivity values between each pair of the electrodes before and after irrigating; and calculating the cracking depth according to the variation conditions of theconductivity values, wherein if the conductivity value has large variation amplitude, the cracking of the depth is more developed, while the conductivity value has small variation amplitude, the cracking of the depth is finely developed. The detecting method cannot destroy the internal structure of the soil mass, and has higher accuracy of the detecting result. The invention also discloses a soilmass cracking depth detecting device.