Abstract: The variation of reflectivity of metal aluminium surface under high power laserinteraction is analysed in this paper.Using an integrating sphere device,the instantaneous varia-tions of the surface reflectivity of aluminium alloys(LY12)irradiated by Q-switched Nd-glasslaser is measured experimentally.The relevant results are obtained for the laser power densities inrange from 10￣6 to 10￣9 W/cm². Meanwhile,the numerical simulation about the relations of alumi-nium conductivity with temperature was conducted based On the free electron model-Drude theo-ry, and it’ s results are in accord with the experiments.When the laser power density is higher(10¹¹～10¹⁶W/cm²),the numerical simulation result of the refleetivity with temperature are ob-tained according to a plasma model and the assumption of local thermal equitibreum(LTE).Theresults are approximate to the experimental results from abroad.