Abstract: In the evaluation of cementing quality, quantitatively assessing cement density is crucial along with identifying the cementation degree at the interface using acoustic logging. While the 137Cs-based formation density logging method is well-suited for density calculation, its reliance on open-hole environmental measurements poses challenges when inspecting cement density. This work focuses on the quantitative calculation of cement density while considering the radioactive hazards to the environment caused by 137Cs source. The proposed approach utilizes a measurement system consisting of an X-Ray source and four gamma detectors. The gamma spectrum characteristics of each detector are analyzed, and the energy spectrum recorded by each detector is distinguished by different energy windows. A forward model is established to relate the gamma counts of each energy window to the formation and cement parameters. By employing a regularized Newton’s method based on optimization technique, cement density can be calculated with a controllable error margin of within 0.015 g/cm3. Furthermore, even though X-Ray detection has lower sensitivity to formation parameters compared to 137Cs, this method is capable of estimating formation density. Overall, the proposed approach enables the quantitative calculation of cement density and semi-quantitative calculation of formation density, therefore is of significance to the comprehensive evaluation of cementing quality.