The metal linear expansion coefficient of metal is studied common physical quantities ,to make amore accurate measurement of metal linear expansion coefficient,it lights amplification principle merged intothe field of measuring metal linear expansion coeficient,using self-made experimental devices such as lighisource ,light screen, heating device, etc. According to the geometric relationship between the reflection angleformed by the light path belore and after heating and the spot position before and after the light screen moves.the small shape variable of the metal is calculated through the moving distance of the spot ,and then the linearexpansion coefficient of the metal is obtained. The linear expansion coefficient of metal is obtained bycalculating the tiny shape varable of metal through the moving distance of the light spot.The average value ofthe linear expansion coefficient of copper is studied ,and compared with the standard value ,the relative error is0.05% ,and the method is extended to the measurement of the linear expansion coefficient of aluminum andtitanium,the relative error is less than 0.90% ,indicating that the method can be used for the measurement ofthe linear expansion coefficient of common metals.