Abstract
The single-mode spin-boson model (SMSBM) has extensive application in different subfields of physics. In the absence of rotating-wave approximation (RWA), we try to solve the SMSBM analytically. We argue that the analytical expression obtained might be the most exact approximation to the solution of the system in our case under the assumption of the Abel-Ruffini theorem, which works for a wide range of the parameters such as coupling strength and detuning and would be practical for currently available experiments.