Two measurement-based methods are presented to quantify the whole-body-averaged specific absorption rate (WBA-SAR) and local SAR for small animals in a medium-size reverberation chamber (RC) for a bio-effect experiment at frequencies above 10 GHz. S-parameter-based method is a totally experimental approach to quantify the WBA-SAR in small animals based on measuring the mean power density and loss power expressed by S-parameters. Two-step method is a measurement-simulation hybrid approach, which links the mean power density to the finite difference time domain (FDTD) calculated WBA-SAR and local SAR in specified organs. However, at a frequency as high as 10 GHz, the RC is usually not ideal because loss on the RC walls is not negligible. In addition, a numerical-only approach is also unrealistic to quantify the SAR because of the heavy calculation burden and difficulty in obtaining converged results. To address this issue, we proposed an improved two-step hybrid method. The method uses the S-parameter-based method to derive the mean power density by matching its WBA-SAR to that of the two-step hybrid method, and then calculate the local SAR in anatomical numerical animal models using the two-step hybrid method under this mean power density. In such a way, in addition to the advantage of obtaining local SAR, the two-step hybrid method has significantly improved its accuracy of SAR quantification.