Abstract: Microcantilever-based structures can be widely applied in Micro-Electro-Mechanical System and Nano-Electro-Mechanical System (MEMS and NEMS). In the practical application, the dynamical response of the cantilever strongly depends on the properties of coating film and surrounding medium. Based on the photothermal vibration model of bilayer microcantilever immersed in fluids, the dynamical responses of coating microcantilever were analyzed. The expressions for temperature, photothermal driving force and dynamical deflection fields were obtained analytically and showed graphically. Theoretical analysis showed that fluids, especially the liquids, have a significant influence on the vibration frequency spectra of microcantilever. Also it could be concluded that when the cantilever vibrated in air, the resonant frequency has a small shift (0.7%) to lower frequencies and resonant peak has almost no change compared to the response in vacuum. However, when the cantilever vibrated in liquids, the resonant frequencies have a distinct shifts (58～80%) to lower frequencies and resonant peaks are distorted, and quality factor decreased on the order of magnitude. This study can be of value to users and designers of microcantilever-based structures in micro-nano detections and AFMs.