It is known that a kind of stall precursor-suppressed (SPS) casing treatment can be used to enhance compressor stall margin (SM) without recognizable efficiency loss. The further requirement in this regard is to develop an effective way to determine the variation range of the SM improvement during the design of such SPS casing treatment. In this investigation, based on the extrapolation hypothesis and the existing work, an extended stall inception model for quantitative evaluation of the SM enhancement is presented for both subsonic and transonic compressors with the SPS casing treatment. The capability of the extended model to quantitatively evaluate the SM enhancement with the SPS casing treatment is validated against the experimental data. The quantitative evaluation results show that the SPS casing treatments with different geometric parameters can improve the SM by a diverse percentage. In particular, for the facilities used in the present investigation, the experiments show that the SPS casing treatments can cause relevant increases of the SM. The change trend of the SM enhancement with various design parameters of the SPS casing treatment is in line with the corresponding theoretical results.