The invention discloses a four-probe scattered gamma-ray logging and linear data inversion method and device. The method comprises steps as follows: acquiring a function relation between detector counting rate and casing thickness; acquiring a function relation between the detector counting rate and cement sheath density; acquiring a function relation between the detector counting rate and cement sheath thickness; solving the casing thickness value, the cement sheath density value, the cement sheath thickness value and stratum density value respectively with an inversion method. According to the method and the device, the three parameters including the casing thickness, the cement sheath density and stratum density can be accurately acquired under certain conditions, so that density logging and cement bond evaluation of a cased well are realized, and theoretical basis is provided for development of a scattered gamma-ray logging instrument for the cased well.