Abstract As oil and gas exploration and development gradually expand into complex areas such as deep and ultra-deep, offshore, and unconventional resources, directional drilling and horizontal wells have become the main methods for increasing reserves and production in petroleum engineering. To address the challenging task of quantitatively evaluating downhole weight on bit (DWOB) and friction drag during sliding drilling in these types of wells, this study proposes a novel method for back-calculation by combining the rate of penetration (ROP) equation with sliding drilling footage. Based on the drilling parameters of the composite drilling phase and the rate of penetration, the ROP equation is established, the downhole weight on bit is estimated based on the drilling parameters of the sliding drilling phase and the ROP. In light of the drilling parameters of the composite drilling phase and the rate of penetration, the ROP equation is established through equation fitting by the least squares method. The downhole weight on bit is estimated on the basis of the drilling parameters of the sliding drilling phase and the ROP. Then the axial friction drag of drilling tools is estimated by combining with the surface weight on bit without the need to equip with the measurement of pup joint. This method enables real-time analysis of sliding drilling efficiency and quantitative estimation of friction drag, with the capability to identify friction reversal trends at formation interfaces. Field results demonstrate that it can effectively capture both gradual and abrupt anomalies in friction behavior. Following mitigation measures, the calculated axial friction drag was reduced by 3.86–90.15%, highlighting the method’s sensitivity to complex downhole conditions and its practical value in improving drilling tool performance. It provides dynamic insight into sliding drilling efficiency and quantitative friction assessment, offering theoretical support for optimizing drilling efficiency, enhancing bottom-hole tool loading, and evaluating the effectiveness of friction-reduction technologies.