Abstract We theoretically investigate the infrared absorption of polaron with spin-orbit coupling in monolayer transition metal dichalcogenides, in which the polaron states are formed arising from the electron coupled with the intrinsic longitudinal optical phonon and the induced surface optical phonon modes. We find that the magnitude of optical absorption are different for the polaron with spin-up and spin-down states in the same valley. Moreover, the absorption peaks of spin-up and spin-down states show the opposite changing trends with increasing the strength of Rashba spin-orbit coupling. These results indicate that the polaron spin state could be used for an effective valley information carrier in two-dimensional valleytronic materials by the infrared optical absorption, which offers new opportunities for potential applications in infrared and valleytronic devices.