Laser-induced chemical etching of Al thin film is investigated. The process is based upon moderate local heating by tightly focused $Ar^+$ laser beam to activate an etching reaction in mixtures of phosphoric acid and nitric acid. The etching rates of Al thin film of the function of the incident laser beam power are measured by the method of extrapolation in the graph of the square of etched hole diameter versus exposure time of laser beam. The spatial distribution of the temperature induced by a cw laser beam absorbed in a thin film in aqueous solution is calculated from the steady-state thermal diffusion equation. However, since decreasing of the film thickness leads to the change of the temperature on the film surface, we introduce the concept of mean temperature which plays the role of the effective temperature during the etching process. Then, the incident laser beam power is converted into mean temperature on the thin film. And Arrhenian temperature dependent of Al etching rate calibrated by mean temperature is correct in various concentrations of etchant and film thicknesses. Enhancements in etching rates up to $10^4$ to $10^6$, compared to background rates, have been observed in the region of laser irradiation. The activation energy of Al thin film is observed 0.72 eV/molecule.