The application provides a method for measuring soil layer thickness based on magnetic susceptibility, which relates to the technical field of soil erosion monitoring. Including: Determination of the original magnetic susceptibility K of the topsoil layer of the sample point b ; Determination of the maximum magnetic susceptibility K of the magnetic piece placed in the topsoil layer m ; Buried magnetic parts at a preset depth below the sample point soil to form a magnetosphere; measure the first magnetic susceptibility K of the topsoil layer directly above the magnetosphere 1 ; After a preset time interval, measure the second magnetic susceptibility K of the topsoil layer directly above the magnetosphere 2 ; According to the conversion equation of the magnetic susceptibility of the soil layer and the thickness of the soil layer, the change value of the soil layer thickness is calculated. The method for measuring the thickness of the soil layer based on the magnetic susceptibility provided by this application has little or no disturbance to the soil layer of the sample point, can quickly and accurately obtain the measurement results, does not require any special manual maintenance, and the soil layer of the sample point is representative , It has strong practicability in soil resource protection, soil erosion monitoring scientific research and field monitoring.